Dip fish in flour, salt and pepper mixture.
Place in a buttered 12 x 8 inch baking dish.
Melt butter in saucepan, add onion and saute until tender.
Remove from heat, add lemon juice, parsley, sour cream and cheese.
Spread over fish.
Sprinkle with crumbs.
Bake 375° for 30 to 40 minutes.