Preheat oven (electric cooker: 225 °C/circulating air: 200 °C/gas: level 4). Clean, wash and cut the peppers into large pieces. Peel and chop onion. Fry both in hot oil, turning frequently for approx. 5 minutes. Season with salt, pepper and thyme
Wash the fish, pat dry and cut into 4 pieces. Sprinkle with lemon juice. Mix sour cream and milk. Season with salt and sweet paprika
Fill the paprika and onion into a greased casserole dish. Season fish with salt and pepper and place on top. Pour sour sour cream over it. Bake in a hot oven for 15-18 minutes, garnish. Serve with mashed potatoes
If you like, you can stir some grated cheese (e.g. from the bag) under the sour cream