Quando estou com pressa, eu como uma torrada com queijo.

Because estar is used for a temporary state or condition, and being in a hurry is temporary. So estou com pressa means I am in a hurry.

Using ser here would be wrong. Sou is for more permanent identity or characteristics, like sou inglês (I am English) or sou alto (I am tall).

Quando estou uses the present indicative and fits a habitual meaning: whenever I’m in a hurry, I eat...

That is exactly what this sentence is doing: it describes a usual pattern.

Quando estiver uses the future subjunctive and would normally refer to a future situation, for example:

• Quando estiver com pressa amanhã, como qualquer coisa rápida.

So for a general habit, quando estou is the natural choice.

Literally, com pressa means with hurry, but idiomatically it means in a hurry.

This is a very common Portuguese expression:

• Estou com pressa. = I’m in a hurry.
• Ele está com pressa. = He’s in a hurry.

You can also hear ter pressa, as in tenho pressa, which also means to be in a hurry.

Because pressa is part of a fixed expression here: estar com pressa.

Portuguese often uses nouns without an article in common expressions of this kind. So you just learn com pressa as the normal phrase, not com a pressa.

Yes. In Portuguese, the subject pronoun is often omitted because the verb ending already shows the subject.

So these are both natural:

• Quando estou com pressa, eu como uma torrada com queijo.
• Quando estou com pressa, como uma torrada com queijo.

Including eu can add a little emphasis, contrast, or just make the subject clearer. In learner materials, pronouns are also often included more than native speakers would always use them.

No. Here como is the verb comer (to eat) in the first person singular present:

• eu como = I eat

Portuguese como can also mean how, but not in this sentence. Here it comes after eu and clearly functions as the verb.

Because the sentence expresses a habitual action, not just something happening right now.

So eu como here means something like:

• I eat
• I usually eat
• Whenever this happens, I eat...

Portuguese often uses the simple present for habits and routines.

Because torrada is being treated as a countable item or serving here, so uma is natural.

• uma torrada = a toast / a piece or serving of toast

If you said just como torrada, it would sound more general, like I eat toast as a type of food, not I eat a toast in that situation.

Not necessarily.

In Portugal, uma torrada often means one serving of toast, especially in a café. That serving may not match exactly what an English speaker imagines as one slice.

So it is best to understand uma torrada as a toast / a serving of toast, not always as one precise slice.

Because com queijo means with cheese: the cheese is something added to or eaten with the toast.

• torrada com queijo = toast with cheese

De queijo usually means of cheese or made with cheese as its defining type, not simply with cheese added.

So in this sentence, com is the normal preposition.

Because queijo is being used in a general, non-specific sense.

• com queijo = with cheese
• com o queijo = with the cheese (a specific cheese already known in the conversation)

This is very common with food nouns in Portuguese.

Yes. That is also correct.

The difference is mainly one of focus:

• Quando estou com pressa, eu como... puts the condition first.
• Eu como... quando estou com pressa starts with the main action.

Both are natural. The original version sounds very normal and sets the situation first.

Because Quando estou com pressa is an introductory subordinate clause.

In standard writing, when this kind of clause comes first, it is usually followed by a comma:

• Quando estou com pressa, eu como...

If the clause comes after the main clause, the comma is often not used:

• Eu como uma torrada com queijo quando estou com pressa.

Yes. Tenho pressa is also very common and natural in European Portuguese.

So both work:

• Quando estou com pressa...
• Quando tenho pressa...

They are very close in meaning. Estar com pressa emphasizes your current state; ter pressa is also a normal everyday way to say to be in a hurry.