Si queda medio pimiento, guárdalo en un recipiente y ciérralo bien.

Because quedar here means to remain / to be left over, which fits the situation very naturally.

• Si queda medio pimiento = If half a pepper is left
• Si hay medio pimiento = If there is half a pepper

Both can make sense in some contexts, but quedar is more idiomatic when you mean something is left over after using part of it.

For example:

• Queda pan = There is bread left
• No queda leche = There’s no milk left

So si queda medio pimiento sounds like: after cooking, if you still have half a pepper remaining.

Here medio means half and works like an adjective before the noun:

• medio pimiento = half a pepper

In Spanish, you normally do not say un medio pimiento in this sense.

Other examples:

• media cebolla = half an onion
• medio limón = half a lemon

You could also say:

• la mitad de un pimiento = half of a pepper

That is also correct, but medio pimiento is shorter and very common.

Because pimiento is a masculine noun:

• el pimiento
• therefore: medio pimiento

If the noun were feminine, you would use media:

• media cebolla
• media naranja

So medio/media agrees with the noun in gender.

Because the subject is singular: medio pimiento.

So the verb agrees with that singular subject:

• queda medio pimiento = half a pepper remains

If it were plural, the verb would change:

• quedan dos pimientos = two peppers remain
• quedan unas sobras = some leftovers remain

Because in affirmative commands, object pronouns are attached to the end of the verb in Spanish.

So:

• guarda + lo → guárdalo
• cierra + lo → ciérralo

This is very common with commands:

• cómelo = eat it
• míralo = look at it
• abrela = open it

In negative commands, the pronoun goes before the verb instead:

• No lo guardes
• No lo cierres

Because when the pronoun is attached, the stress pattern changes, and Spanish adds an accent mark to keep the original stress in the right place.

Compare:

• guarda → stress on guar
• guárdalo → the stress still needs to stay on guar
• cierra → stress on cie
• ciérralo → the stress stays on cie

Without the accent marks, a reader might stress them incorrectly.

This is a very common rule with commands + attached pronouns.

Lo refers to medio pimiento — the half pepper that is left.

Because pimiento is masculine singular, the direct object pronoun is:

• lo

So:

• guárdalo = store it
• ciérralo = close it

If the noun were feminine, you would use la instead:

• media cebolla → guárdala

Because this sentence is using the tú command, which is the informal singular command in Spain.

• guarda = keep/store
• cierra = close

With pronouns:

• guárdalo
• ciérralo

If you wanted the formal usted version, it would be:

• guárdelo
• ciérrelo

So this sentence is speaking to someone in a normal informal way, like a recipe, household instruction, or everyday advice.

Because after si for a real or likely condition, Spanish normally uses the indicative, not the subjunctive.

So:

• Si queda medio pimiento, guárdalo = If half a pepper is left, store it

This is a normal real condition.

Compare:

• Si llueve, nos quedamos en casa = If it rains, we’ll stay home

Spanish does not say:

• Si quede... ❌

The subjunctive is not used after si in this kind of basic conditional sentence.

Here guardar means something like:

• to put away
• to store
• to keep

In kitchen context, guárdalo en un recipiente means:

• put it in a container and keep it there
• store it for later

It does not mean guard in the English sense of protecting something physically.

Very common uses:

• Guarda la comida en la nevera = Put the food away in the fridge
• Guarda esto para mañana = Save this for tomorrow

Recipiente is a general word meaning container.

So:

• en un recipiente = in a container

It is completely correct and neutral.

In everyday Spain Spanish, people also very often say:

• un táper = a plastic food container

So in casual speech, you might hear:

• Guárdalo en un táper

But recipiente is broader and works in all contexts, including instructions and written Spanish.

Here bien means well / properly / tightly.

So:

• ciérralo bien = close it properly / seal it well

In English we often use well less often in this kind of sentence, but in Spanish it is very natural to add bien to stress that it should be securely closed.

Other examples:

• Lávate bien las manos = Wash your hands well
• Tápalo bien = Cover it well
• Mézclalo bien = Mix it well

In Spain, pimiento usually means pepper, and in many cooking contexts it often refers to a bell pepper / sweet pepper, unless the context says otherwise.

So:

• pimiento rojo = red pepper
• pimiento verde = green pepper

If you specifically mean a hot chili pepper, Spanish in Spain may use words like:

• guindilla
• pimiento picante

So in this sentence, most learners would understand pimiento as an ordinary cooking pepper, probably a bell pepper.

Yes. Sobrar is also very natural here.

• Si queda medio pimiento = If half a pepper is left
• Si sobra medio pimiento = If half a pepper is left over

Both are good, but there is a slight nuance:

• quedar focuses on what remains
• sobrar focuses more on what is extra / left over

In many kitchen contexts, both sound perfectly normal.