Si vols, talla el pebrot molt petit i posa'l sobre l'enciam.

Yes. Si vols literally means if you want.

In this kind of instruction, it often works as a softener, like:

• If you like
• If you want
• If you’d like to

So it makes the instruction sound less direct. It is addressed to tu singular, informal.

Catalan usually drops subject pronouns when they are not needed, because the verb ending already shows who the subject is.

So:

• vols = you want
• talla = cut! addressed to you
• posa = put! addressed to you

You could add tu for emphasis, but normally you would not:

• Si tu vols... = more emphatic, less neutral

They are imperative forms, used for commands or instructions.

Here they are the informal singular imperative forms for tu:

• tallar → talla
• posar → posa

So:

• talla el pebrot = cut the pepper
• posa'l sobre l'enciam = put it on the lettuce

This is very common in recipes and instructions.

Because Catalan uses a direct object pronoun to avoid repeating the noun.

• el pebrot = the pepper
• el = it referring to the pepper

So instead of repeating el pebrot, Catalan says:

• posa'l = put it

This is the same idea as English put it, not put the pepper again.

In Catalan, with an affirmative command, object pronouns are normally attached to the end of the verb.

So:

• el posa = he/she puts it
• but posa'l! = put it!

This is a standard rule:

• with normal finite verbs, pronouns usually go before the verb
• with positive imperatives, they go after the verb

Examples:

• Ho fa = he/she does it
• Fes-ho = do it

The apostrophe shows that the pronoun el has been shortened before being attached to a verb ending in a vowel.

• full pronoun: el
• after posa → posa'l

So posa'l is basically:

• posa + el

This is just the normal written form to avoid awkward vowel contact.

Molt petit literally means very small.

In this sentence, it means something like:

• cut the pepper very small
• cut the pepper into very small pieces
• cut the pepper finely

Catalan often uses an adjective phrase like molt petit where English might prefer an adverb such as finely. So it sounds natural in Catalan even though the English structure is a bit different.

Both nouns take the masculine singular definite article:

• el pebrot = the pepper
• el enciam = the lettuce

But before a vowel sound, el becomes l':

• el + enciam → l'enciam

So:

• el pebrot
• l'enciam

This is the same article, just in two different forms.

Catalan often uses the definite article with ingredients and food items in instructions where English may or may not use the.

So in a recipe context, el pebrot and l'enciam sound completely natural.

Using the article can make the ingredient sound like the specific one you are working with in the recipe:

• talla el pebrot
• posa'l sobre l'enciam

This is very normal Catalan usage.

Sobre means on, on top of, or over, depending on context.

Here:

• sobre l'enciam = on the lettuce / on top of the lettuce

In a food context, it means the pepper should be placed on the lettuce, not necessarily physically hovering over it.

Yes, this sentence is informal singular, addressed to tu.

Informal singular:

• Si vols, talla el pebrot molt petit i posa'l sobre l'enciam.

A formal singular version using vostè would be:

• Si vol, talli el pebrot molt petit i posi'l sobre l'enciam.

An informal plural version using vosaltres would be:

• Si voleu, talleu el pebrot molt petit i poseu-lo sobre l'enciam.

Notice that the pronoun form can also change in spelling when attached:

• posa'l
• poseu-lo

That depends on the verb form and sound combination.