The Portuguese present tense also translates to the English progressive form and it can be helpful to remember this at times. Eu cozinho = I cook. Eu cozinho = I am cooking. Duo thus accepts 'I am cooking a sauce.' as a valid answer to this question. Eu falo = I speak = I am speaking.
Yes, pfeil, both languages have present progressive tenses, but they aren't always used in exactly the same way. That's why Duolingo will often accept, as Lahure said, "I am cooking" for "Eu cozinho" as well as for "Eu estou cozinhando". It's not wrong - and remember that using caps lock can often look like yelling, so use it sparingly.
In fact you're right, it does not always translates the same way. But the only situation I can reckon this statement is true is when using the Present progressive/continuous tense for future arrangements: "Eu cozinho pra você amanhã" = "I'm cooking for you tomorrow" (if one wants to know the Simple future tense: "Eu vou cozinhar pra você amanhã" = "I will / am going to cook for you tomorrow") It is also important to say that Portuguese is more complex in this topic, because it would be strange "eu estou cozinhando pra você amanhã", but it is totally fine to say "eu estou indo embora amanhã" ("I'm leaving tomorrow").