Salt and pepper the fish and drizzle with lemon juice. Peel the onions and cut them into rings. Wash and clean the peppers, cut in half, remove the seeds, remove the white skins and cut into fine strips. Sweat the onions in hot butter until translucent and cook for about 4 minutes. Then put half of it in a baking dish, then spread the fish over it. Peel, quarter and core the apples, cut into wedges and spread over the fish with the remaining vegetables, mix the dill with sour cream, season with salt, pepper and paprika powder and place on the casserole. Cook in a preheated oven (200 ° C) for about 40 minutes.