"FOI": 1) It could be the past tense for "ir" (to go) Ex: Ele foi à praia. (He went to the beach). 2) It could be the past tense for "ser" (to be) when it refers to something that someone was and is no longer (because they died or they are not doing that kind of stuff anymore). Ex: Ele foi um bom pai. (He was a good father) Ex: Ele foi um bom funcionário, enquanto trabalhou aqui. Agora está em outro emprego. (He was a good employee when he worked here. Now he works somewhere else. ''ESTAVA'': 1) It is the imperfect past tense for ''ser'' (to be). It is used to express an action that was happening in the past, in a continuous manner. It is also used to describe the background of a story being narrated or even someone's mood. Ex: Eu estava triste. (I was sad.) Ex: Eu estava fazendo o jantar quando ela chegou. (I was making us dinner when she arrived) Ex: Estava muito frio naquele dia (It was very cold that day)

Both ways are good. But the second one carries an ''impatient'' tone with it. It seems like the person asking is in a hurry to have their fish as soon as possible. But this can be avoided by asking it while smiling or any other body language and it depends on the context. Be careful with the verb use there. The correct form is "preparar". When this phrase is spoken, we usually don't say the ''R'' at the end, but when you are writing, the correct way to do it is with the ''r''.