Saute onions, mushrooms, celery and pepper in half of the butter.
Add bread crumbs and the rest of the butter.
Mix and season with half of the lemon juice.
For each fillet, place a handful of stuffing in the center and roll up the fillet.
Place the rolled fillets in a lightly greased baking dish.
Dot them with butter and the rest of the lemon juice.
Sprinkle them with garlic salt and paprika.
Bake at 350 degrees for 25 minutes.