Kad imam više vremena, pečem brokulu i cvjetaču u pećnici s malo ulja.

Because Croatian usually leaves out subject pronouns when they are clear from the verb ending.

• imam = I have
• pečem = I bake / roast

So ja is not necessary. You could add ja for emphasis, contrast, or clarity:

• Kad ja imam više vremena, pečem brokulu...
  = When I have more time, I roast broccoli...

But in normal neutral speech, leaving ja out is more natural.

They both mean when.

• kad is shorter and very common in everyday speech and writing.
• kada is a bit fuller and can sound slightly more formal or careful.

In this sentence, both would work:

• Kad imam više vremena...
• Kada imam više vremena...

There is no important change in meaning here.

Croatian often uses the present tense for habitual or general actions, just like English does in sentences such as When I have more time, I roast vegetables.

This sentence describes a repeated or usual situation:

• Kad imam više vremena, pečem...
• When I have more time, I roast...

It does not mean one specific future occasion.

If you wanted a specific future meaning, Croatian would usually change the structure, for example:

• Kad budem imao više vremena, ispeći ću brokulu i cvjetaču.
  = When I have more time, I’ll roast broccoli and cauliflower.

Vremena is the genitive singular of vrijeme (time).

After više meaning more, Croatian usually puts the following noun in the genitive:

• više vremena = more time
• više novca = more money
• više posla = more work

So:

• vrijeme = nominative
• vremena = genitive

That is why imam više vremena is correct.

Yes. In this sentence, više means more:

• više vremena = more time

It is a very common word and can appear in other meanings too depending on context, but here it is simply the comparative quantity word more.

Pečem comes from the verb peći, which means to bake, to roast, or sometimes more generally to cook by heat.

Here, peći is the imperfective verb, which is the normal choice for a habitual or repeated action:

• Kad imam više vremena, pečem...
• When I have more time, I roast...

If you used ispeći / ispečem, that would be the perfective partner and would usually emphasize a completed result, often in a one-time event.

So in this sentence:

• pečem = natural for something I do regularly or whenever I have time
• ispečem = would sound more like one completed roasting event

In this context, English would usually prefer roast:

• pečem brokulu i cvjetaču u pećnici
  = I roast broccoli and cauliflower in the oven

But Croatian peći can cover both bake and roast, depending on what is being cooked.

So the Croatian verb is broader than the English choice. The exact English translation depends on context.

They are in the accusative singular because they are the direct objects of pečem.

Base forms:

• brokula = broccoli
• cvjetača = cauliflower

As direct objects:

• pečem brokulu
• pečem cvjetaču

For many feminine nouns ending in -a, the accusative singular ends in -u:

• žena → ženu
• salata → salatu
• brokula → brokulu
• cvjetača → cvjetaču

Because Croatian does not have articles like English a/an and the.

So Croatian simply says:

• pečem brokulu i cvjetaču

Depending on context, that could correspond to English:

• I roast broccoli and cauliflower
• I roast the broccoli and the cauliflower
• I roast some broccoli and cauliflower

Context tells you which meaning is intended.

Because u can take different cases depending on the meaning:

• u + locative = in / inside (location)
• u + accusative = into (movement toward)

Here the phrase describes the place where the cooking happens:

• u pećnici = in the oven

Compare:

• Stavljam brokulu u pećnicu. = I’m putting the broccoli into the oven.
• Brokula je u pećnici. = The broccoli is in the oven.

So u pećnici is correct because it expresses location.

This means with a little oil.

• s = with
• malo = a little / a small amount of
• ulja = genitive of ulje (oil)

A useful thing to remember is that quantity words like malo are followed by the genitive:

• malo vode = a little water
• malo soli = a little salt
• malo ulja = a little oil

So the whole phrase means:

• s malo ulja = with a little oil

Because Kad imam više vremena is a subordinate clause, and it is separated from the main clause by a comma.

Structure:

• Kad imam više vremena, = subordinate clause
• pečem brokulu i cvjetaču u pećnici s malo ulja. = main clause

This is standard Croatian punctuation.

Yes. Croatian word order is more flexible than English word order. The version you have is neutral and natural, but other orders are also possible if you want a different emphasis.

For example:

• Kad imam više vremena, pečem brokulu i cvjetaču u pećnici s malo ulja.
  Neutral.

• Kad imam više vremena, brokulu i cvjetaču pečem u pećnici s malo ulja.
  Puts more focus on brokulu i cvjetaču.

• Brokulu i cvjetaču pečem u pećnici s malo ulja kad imam više vremena.
  Sounds possible, but the timing clause now comes later.

So yes, the order can change, but the original sentence is the most straightforward version for a learner.