At this time, cut onion and pepper (yellow and red) into long strips. The most important thing is that onions and peppers are in equal proportions. And about a third of the weight of the beans.
In a hot frying pan, fry the first onion very quickly (3-4 minutes), then add pepper. Reduce the heat to medium, fry for another 3-5 minutes.
I will add about baking: I do not use oil. Add a tablespoon of water to the onion (so as not to burn) and fry.