Peel and chop the pepper and onion, then heat them in oil.
We clean and slice the mushrooms. Add them over the hardened onions and peppers. Salt, pepper and let the water left by the mushrooms drop. This will happen over low heat with the pot covered.
Mix the two tablespoons of flour with cold milk, taking care not to remain lumpy, and add this mixture over the mushrooms. The sauce will form quickly, stir constantly. Do not catch the food.
Depending on the preference, we add a little more water (if we like the sauce more liquid). let it simmer for about 10 minutes, simmer the fire and at the end add the washed and finely chopped greens.