Clean and salt the breams and sprinkle them with black pepper. Soak them in 1 cup white wine for 15-20 minutes. Heat oil for frying.
Mix the flour with the garlic powder, ground walnuts. Roll each fish in the mixture and put it to fry evenly on both sides.
In the oil released from the breams, fry up the chopped onions. Once softened, pour in the wine and allow it to reduce.
To the sauce, squeeze in half a lemon and season with salt and black pepper to taste.
Serve the breams on a plate garnished with vegetables, with the sauce in a gravy bowl.