Cuando terminen las obras de la cocina, nos pondremos a preparar salmón con espinacas para invitar a la familia.

Because in Spanish, after cuando referring to a future event, you normally use the present subjunctive, not the future or the present indicative.

So:

• Cuando terminen las obras... = When the building work is finished... / When the renovations are done...

This is a very common pattern:

• Cuando llegue, te llamo. = When he/she arrives, I’ll call you.
• Cuando acabemos, cenamos. = When we finish, we’ll have dinner.

Why not terminarán?
Because Spanish does not usually use the future tense after cuando in this kind of sentence.

Why not terminan?
You can use the indicative after cuando, but usually only for habitual actions or things seen as factual/past/present, not a future completion that has not happened yet.

Because the subject is las obras, which is plural.

• la obra = a work/project/job
• las obras = works / building work / renovation work

So the verb has to match:

• las obras terminan
• cuando las obras terminen

Even though English often uses singular expressions like the building work or the renovation, Spanish commonly uses the plural las obras.

In Spain, las obras very often means building work, renovation work, or construction/repair work being done in a home or building.

So las obras de la cocina means something like:

• the kitchen renovations
• the building work in the kitchen
• the work being done on the kitchen

It does not usually mean artistic works or literary works here. In this context, it is clearly about home renovation.

Both can be possible in different contexts, but they suggest slightly different things.

• las obras de la cocina = the kitchen works/renovations, meaning the works belonging to or affecting the kitchen
• las obras en la cocina = the work in the kitchen, focusing more on the location

In this sentence, de la cocina sounds like the kitchen renovation project as a unit. It is a very natural way to refer to the work being done on that room.

Ponerse a + infinitive means to start doing something, to get down to doing something, or to set about doing something.

So:

• nos pondremos a preparar = we’ll start preparing / we’ll get down to preparing

It comes from the verb ponerse. In this structure, it does not literally mean to put ourselves; it is an idiomatic expression.

Examples:

• Me puse a estudiar. = I started studying.
• Se pusieron a reír. = They started laughing.

So in your sentence, the idea is that once the kitchen works are done, we’ll begin preparing the salmon with spinach.

Because the verb is ponerse, which is a pronominal verb.

The full verb is not just poner here; it is ponerse a + infinitive.

With nosotros, the reflexive/pronominal pronoun is nos:

• me pongo
• te pones
• se pone
• nos ponemos
• os ponéis
• se ponen

In the future:

• nos pondremos

So nos is required because that is how this verb is used in this meaning.

Both are possible, but they are not exactly the same.

• prepararemos salmón... = we will prepare salmon...
• nos pondremos a preparar salmón... = we will start preparing salmon...

The second one emphasizes the beginning of the action. It gives a sense of getting started once the renovations are over.

A close English equivalent would be:

• Once the kitchen work is done, we’ll get started on preparing salmon with spinach...

So it adds a bit more action and timing than a simple future.

Because the whole situation is in the future.

The sentence describes:

1. a future event: the kitchen work finishing
2. another future event after that: we will start preparing the food

So the future tense is natural:

• nos pondremos

That said, Spanish often also uses the present tense to talk about future plans in everyday speech:

• Cuando terminen las obras, nos ponemos a preparar salmón...

This can sound perfectly natural in conversation. But nos pondremos is a bit more explicitly future.

Spanish often leaves out the article when talking about food or ingredients in a general, recipe-like sense.

So:

• preparar salmón con espinacas = to prepare salmon with spinach

This sounds like naming a dish or meal, not referring to a specific already-known salmon or spinach.

If you added articles, the meaning could become more specific depending on context:

• preparar el salmón = prepare the salmon
• con las espinacas = with the spinach

But here, the article-free version is very natural for ingredients.

Para + infinitive expresses purpose:

• para invitar a la familia = in order to invite the family / so as to invite the family

In more natural English, the overall idea is probably:

• to have the family over
• to invite the family round
• to invite the family for a meal

Spanish often leaves some of that implied. The sentence literally says to invite the family, but the intended meaning is likely that the food is being prepared so the family can be invited over.

Yes, it is understandable and possible, but in real life many speakers might make it more explicit, for example:

• para invitar a la familia a comer
• para invitar a la familia a cenar
• para invitar a la familia a casa

These mean:

• to invite the family for lunch
• to invite the family for dinner
• to invite the family over to the house

So the original sentence is fine, but it leaves the final part slightly implicit.

Because invitar takes a direct object, and in Spanish you usually need the article when talking about a specific group like the family.

So:

• invitar a la familia = to invite the family

Also, because the direct object is a person or people, Spanish uses the personal a:

• invitar a María
• invitar a mis amigos
• invitar a la familia

That a is not the same as the article la; it is the personal a required before human direct objects.

Because the sentence begins with a subordinate clause:

• Cuando terminen las obras de la cocina, ...

After that introductory time clause, Spanish often uses a comma before the main clause:

• ..., nos pondremos a preparar...

This is similar to English:

• When the kitchen renovations are finished, we’ll start preparing...

The comma helps separate the time condition from the main action.

Yes, very naturally.

• Cuando terminen las obras...
• Cuando acaben las obras...

Both mean roughly when the works are finished.

A small nuance:

• terminar focuses on ending
• acabar often feels very similar in everyday Spanish and is extremely common in Spain

In many contexts, they are almost interchangeable here.

Usually, yes, when referring to the vegetable as food.

So Spanish normally says:

• espinacas = spinach

Even though English often treats spinach as an uncountable singular noun, Spanish commonly uses the plural form espinacas.

Examples:

• Me gustan las espinacas. = I like spinach.
• Tortilla de espinacas = spinach omelette

So salmón con espinacas is completely normal.

It is understandable everywhere, but a couple of things feel very natural in Spain, especially:

• las obras for home renovations/building work
• the overall phrasing style

Nothing in it is strongly restricted to Spain only, but las obras is especially common in Spain when talking about noisy renovation work in a flat or house.