La pizza con rucola e pomodoro è molto buona.

Because pizza is a feminine singular noun in Italian. The definite article has to match the noun’s gender and number:

• la = feminine singular
• il = masculine singular

So la pizza is correct.

Con means with.

In this sentence, it links pizza to its toppings or ingredients:

• pizza con rucola e pomodoro = pizza with arugula and tomato

In food contexts, con is very common for saying what something contains or is served with.

In Italian, when listing ingredients or toppings, it is very common to use the nouns without articles:

• pizza con rucola e pomodoro
• pasta con tonno
• insalata con pollo

This sounds natural and menu-like.

You could sometimes hear more expanded versions in other contexts, but in a simple ingredient list, leaving out the articles is very normal.

In food descriptions, Italian often uses the singular name of an ingredient in a general sense, even when the food obviously contains more than one piece of it.

So con pomodoro means something like with tomato / tomato as an ingredient.

This is especially common in menu language and simple food descriptions. You may also see plurals in some contexts, but the singular here is completely natural.

The accent is required because è is the verb is from essere.

It is written differently from e, which means and.

So:

• è = is
• e = and

This accent is very important in writing because it changes the meaning.

Because buona is an adjective, and it describes the noun pizza.

• buona = good
• bene = well

In this sentence, you are saying the pizza is good, not that it does something well. So the adjective is needed:

• La pizza è buona. = The pizza is good.
• La pizza è molto buona. = The pizza is very good.

Because the adjective has to agree with pizza, which is feminine singular.

Agreement works like this:

• masculine singular: buono
• feminine singular: buona
• masculine plural: buoni
• feminine plural: buone

Since pizza is feminine singular, the correct form is buona.

Molto means very here. It strengthens the adjective buona:

• buona = good
• molto buona = very good

So molto is functioning as an adverb modifying the adjective.

Yes. Rucola is the Italian word for arugula.

In British English, it is also often called rocket.

So if you are connecting the vocabulary:

• rucola = arugula / rocket

Yes. That would still be perfectly correct.

• è buona = is good
• è molto buona = is very good

Adding molto just makes the praise stronger.

Because the sentence is using essere to link the subject to a description:

• La pizza = the subject
• è = is
• molto buona = the description

This is the normal pattern:

subject + essere + adjective

So La pizza è molto buona works just like The pizza is very good in English.