На обед мы запекли брокколи и цветную капусту с сыром.

На обед means for lunch.

Russian often uses на + accusative with meals:

• на завтрак = for breakfast
• на обед = for lunch
• на ужин = for dinner

So На обед sets the context first: this is what they made for lunch.

Also, обед here is in the accusative case, but because it is a masculine inanimate noun, its accusative form looks the same as the nominative: обед.

Запекли is the perfective past form of запечь.

Perfective is used because the speaker presents the action as:

• a completed whole
• a finished result

So мы запекли... means they baked/roasted it and finished doing so.

By contrast, запекали would be imperfective and would suggest:

• process
• repeated action
• background description

For example:

• Мы запекали брокколи весь вечер. = We were baking broccoli all evening.
• На обед мы запекли брокколи... = For lunch we baked broccoli...

Because the subject is мы = we.

Russian past tense agrees in number, and in the singular also in gender:

• я запёк / я запекла
• он запёк
• она запекла
• мы запекли

So запекли is simply the correct past plural form for мы.

Yes. Russian often drops subject pronouns when they are clear from the verb form.

So both are possible:

• На обед мы запекли брокколи и цветную капусту с сыром.
• На обед запекли брокколи и цветную капусту с сыром.

The form запекли already tells you the subject is we or sometimes an unspecified they depending on context.

Including мы can add:

• clarity
• emphasis
• contrast

For example, мы may suggest we did it ourselves.

Because цветная капуста is the direct object of the verb запекли, so it goes into the accusative case.

Dictionary form:

• цветная капуста = cauliflower

Accusative singular:

• цветную капусту

Both words change because this is a feminine singular noun phrase:

• цветная → цветную
• капуста → капусту

So:

• Мы запекли цветную капусту. = We baked cauliflower.

Because брокколи is an indeclinable noun in Russian.

That means its form usually stays the same across cases:

• nominative: брокколи
• accusative: брокколи
• after many prepositions: still брокколи

So even though it is also a direct object after запекли, it does not visibly change.

Learners often notice that this makes брокколи look easier than цветная капуста, which has normal case endings.

С сыром is in the instrumental case.

The preposition с often means with, and when it means accompaniment or an added ingredient, it commonly takes the instrumental:

• с сыром = with cheese
• с мясом = with meat
• с овощами = with vegetables

Here:

• dictionary form: сыр
• instrumental singular: сыром

So с сыром means the vegetables were baked with cheese.

Most naturally, it describes the whole dish: broccoli and cauliflower with cheese.

In other words, Russian speakers will usually understand:

• [брокколи и цветную капусту] с сыром

rather than:

• broccoli, and only the cauliflower had cheese

That said, like in English, the ending phrase can be a little structurally loose in some contexts. If you wanted to make it absolutely clear that only the cauliflower had cheese, you would usually rephrase.

For example:

• На обед мы запекли брокколи, а цветную капусту — с сыром.

Russian word order is fairly flexible, so the basic meaning would stay the same in several versions.

For example:

• На обед мы запекли брокколи и цветную капусту с сыром.
• Мы запекли на обед брокколи и цветную капусту с сыром.
• Брокколи и цветную капусту с сыром мы запекли на обед.

What changes is mostly the focus or emphasis.

In this sentence, starting with На обед gives the time/purpose frame first:

• As for lunch, we baked...

That sounds natural and very common in Russian.

Not always exactly.

Запечь / запекать usually means something like:

• to bake
• to roast
• to cook in the oven until browned or finished

It often suggests oven cooking, especially with a finished top or crust.

So in food contexts, English translations may vary:

• bake
• roast
• oven-bake

The best translation depends on the dish, but grammatically the Russian verb is the right one for vegetables cooked in the oven, especially with cheese.

Literally, yes:

• цветная = colored / flowering
• капуста = cabbage

But as a fixed expression, цветная капуста simply means cauliflower.

This is a good reminder that literal word-by-word meanings are not always the best way to understand vocabulary. In actual usage, Russian speakers do not think of it as an odd phrase; it is just the normal word for cauliflower.