DL is a bit inconsistent in this. It definitely prefers the more common word order for questions (i.e. "Are you...?" rather than "You are...?")
The problem is that the same questions get used going from English to Spanish and vice versa, so whilst the "You are...?" form is technically correct, DL wants to emphasise that the word order in English normally switches when going from a statement to a sentence, whereas in Spanish it does not.
If you want to avoid getting pinged, use the more common English word order for questions. I.e. Verb pronoun - Are you, Do we, Can she, Will he, Have they, Should I, ... etc.
Thanks for helping me understand DL better. And for understanding why a certain translation is the one that is favored and considered correct. I too had written "You are cooking an onion?" I like the emphasis this gives! It is when one is surprised by the fact that the person is cooking. Rather than the more common question of just asking if an onion is being cooked. I took it to be an emphasis on the person rather than the action.
I put the question marks to show that it was a question. I know the vocabulary. Need more fine tuning...
Sometimes, Duo misses what I say completely. I use a headset, with ear-phones and a boom mic. First I unplug the mic and plug it back in. If it continues to "mishear"me, I go the mic/record set up (Windows) in Control Panel (under Sound, I think), and recalibrate the mic. There is an app there for listening while you read a short paragraph and Windows sets the levels for dictation. That would apply to both on-board and plug-in mics. I suppose that Apple devices have something similar, or maybe they're advanced enough to automatically do it.
I use a plug-in headset (ear-phones & mic in one unit), because the cheap mic on my laptop doesn't pick up the sound good enough, and the speaker is just as bad. I like listening to music, so I bought a good headset. Generally speaking, while the speakers/earphone on a headset vary wildly in quality (you get what you pay for), the mics are all pretty much the same. You have to pay hundreds of $$$ for even a moderately better mic than the cheap plug-ins that used to come with every desktop. But the cheap mics all do a great job, which include the ones in laptops - it's just a question of distance from you mouth, mic location, possible interference of the aperture in the computer casing, and proper calibration by the system.
I knew that it meant "cooking," but the drop-down hints said that "cocinando" also means "boiling." I tried that, but surprise, surprise, despite giving that as a possible answer, Duolingo doesn't accept it! I wish to hell that Duolingo would stop providing answers that it refuses to accept!