Halibut Fillet with Avocado

Preheat oven to 350°F.
Cut halibut fillets into serving size pieces.
Lay the halibut single layer into a greased baking dish.
Melt the butter in a pan, add mushrooms and onions, and saute.
When the onions are tender, add the bread crumbs, salt, pepper, parsley, and celery salt and mix well.
Combine the egg and lemon juice in a dish and brush the fish with it.
Peel and slice the avocado and arrange over the fish.
Top with bread crumb mixture.
Sprinkle with cheese.
Bake for 35 minutes or until fish flakes easily when tested with fork.