Clean and halve the onion, then cut into strips. Clean the red pepper and cut into strips.
Heat margarine in a saucepan over high heat. Fry the onion and red pepper strips for 2 minutes. Add the sauerkraut, season with salt and pepper, and stew for 4 minutes over high heat.
While the vegetables cook, cut the cod fillets into bite-sized pieces, drizzle with the lemon juice, and season with salt.
Spread the sauerkraut mixture in an ovenproof dish, arrange the cod pieces on top, season the whipped cream with paprika powder, pour it over the fish, and bake for 20 minutes at 200 °C (392 °F).
Serve sprinkled with chopped parsley, with mashed or boiled potatoes on the side.