Hoy quiero cocinar lentejas con verduras porque las lentejas me llenan bastante y son baratas.

Quiero cocinar means I want to cook.

• quiero = I want
• cocinar = to cook

So this structure is:

querer + infinitive = to want to do something

If you said Hoy cocino lentejas..., that would mean Today I’m cooking lentils... or Today I cook lentils..., which is more direct and sounds like a statement of what you are doing, not what you want to do.

Spanish often puts time expressions like hoy, mañana, esta noche, etc. at the beginning for emphasis or simply because it sounds natural.

So:

• Hoy quiero cocinar lentejas... = Today I want to cook lentils...

You could also say:

• Quiero cocinar lentejas hoy...

Both are correct, but starting with Hoy sets the time frame immediately.

In Spanish, subject pronouns are often omitted because the verb ending already shows who the subject is.

• quiero clearly means I want

So (yo) quiero is usually just quiero.

You can include yo if you want emphasis or contrast:

• Yo quiero cocinar lentejas, pero él no.
  I want to cook lentils, but he doesn’t.

But in a normal sentence, leaving it out is more natural.

In Spanish, when talking about food or things in a general, indefinite way, the article is often omitted after verbs like cocinar, comer, comprar, etc.

So:

• cocinar lentejas = to cook lentils

This sounds natural and general, like saying what kind of dish you want to make.

If you said cocinar las lentejas, it would usually refer to some specific lentils already known in the context.

Here las lentejas is being used in a general sense to talk about lentils as a type of food.

Spanish often uses the definite article with nouns when talking about things in general:

• Las lentejas son baratas. = Lentils are cheap.
• El café me gusta. = I like coffee.
• Los perros son inteligentes. = Dogs are intelligent.

So even though English often uses no article for general statements, Spanish frequently uses el/la/los/las.

Porque (one word, no written accent) means because.

That’s what we need here:

• ...porque las lentejas me llenan bastante...
• ...because lentils fill me up quite a lot...

Por qué (two words, with an accent on qué) means why in direct and indirect questions:

• ¿Por qué quieres cocinar lentejas? = Why do you want to cook lentils?
• No sé por qué quiere cocinar lentejas. = I don’t know why he/she wants to cook lentils.

So:

• porque = because
• por qué = why

Literally, me llenan means they fill me.

In natural English, here it means:

• they fill me up
• they are quite filling
• they make me feel full

Breakdown:

• me = me
• llenan = they fill

The subject is las lentejas, which is plural, so the verb is plural too:

• las lentejas llenan
• las lentejas me llenan

This is a very natural way in Spanish to say that a food is filling.

Because the subject is plural:

• las lentejas = the lentils

So the verb must also be plural:

• las lentejas me llenan

Compare:

• La sopa me llena. = The soup fills me up.
• Las lentejas me llenan. = Lentils fill me up.

Singular subject → singular verb
Plural subject → plural verb

Here bastante means something like:

• quite a lot
• pretty well
• fairly much

So me llenan bastante means:

• they fill me up quite a lot
• they’re pretty filling

It softens the statement a little. It is not as strong as saying muchísimo, but stronger than saying nothing.

Examples:

• Me gusta bastante. = I like it quite a lot.
• Es bastante caro. = It’s quite expensive.

In this sentence, son baratas means they are cheap in a general sense.

Use ser for a general characteristic:

• Las lentejas son baratas. = Lentils are cheap.

Use estar more for a temporary condition, a current price, or a special offer:

• Hoy las lentejas están baratas en ese supermercado.
  Today lentils are cheap in that supermarket.

So here, the idea is that lentils are generally an inexpensive food, so son baratas is the natural choice.

Because baratas must agree with las lentejas, which is:

• feminine plural

So the adjective also becomes feminine plural:

• baratas

Agreement pattern:

• el libro barato = masculine singular
• la sopa barata = feminine singular
• los libros baratos = masculine plural
• las lentejas baratas = feminine plural

Even though lentils in English are not thought of as feminine, the Spanish noun lenteja is feminine: la lenteja.

Con verduras means with vegetables in a general sense.

When Spanish talks about ingredients in a non-specific way, it often leaves out the article:

• arroz con pollo
• pasta con tomate
• lentejas con verduras

This means the dish includes vegetables, but we are not talking about specific vegetables already mentioned.

If you said con las verduras, it would usually suggest specific vegetables known from the context:

• Voy a cocinar las lentejas con las verduras que compré ayer.
  I’m going to cook the lentils with the vegetables I bought yesterday.

You could, but in Spain verduras is usually the more natural word in this kind of cooking context.

• verduras = vegetables, especially as food/ingredients
• vegetales can exist, but it often sounds more technical, broader, or less natural in everyday cooking speech

So for a dish like this, lentejas con verduras is the normal phrase in Spain.

Spanish often repeats the noun instead of using a pronoun like ellas, especially when it sounds clearer or more natural.

So:

• ...porque las lentejas me llenan bastante y son baratas

sounds very natural.

If you replaced it with ellas, it would usually sound more marked or unnecessary unless you were contrasting them with something else.

Spanish tends to prefer repeating the noun more often than English does.

Because once the subject las lentejas has already been stated, Spanish can omit it if it is still clearly the same subject.

So:

• las lentejas me llenan bastante y son baratas

means:

• lentils fill me up quite a lot and are cheap

The subject for both verbs is las lentejas:

• las lentejas me llenan
• (las lentejas) son baratas

Repeating the subject again would still be grammatical, but less smooth:

• ...porque las lentejas me llenan bastante y las lentejas son baratas

That sounds unnecessarily repetitive.

The sentence uses the present tense:

• quiero = present
• llenan = present
• son = present

Spanish often uses the present tense in the same kinds of ways English does here:

• Hoy quiero cocinar... = what I want today
• Las lentejas me llenan... = a general fact about how lentils affect me
• Son baratas = a general fact about lentils

So this is a mix of:

• a present desire/intention
• general truths or habits

A more literal breakdown would be:

• Hoy = today
• quiero cocinar = I want to cook
• lentejas con verduras = lentils with vegetables
• porque = because
• las lentejas = lentils
• me llenan bastante = fill me up quite a lot / are quite filling
• y son baratas = and are cheap

So a close natural rendering is:

Today I want to cook lentils with vegetables because lentils are quite filling and cheap.

That also helps show how the Spanish grammar is working.