Cover bottom of baking dish with halibut fillets (or steaks).  Fry bacon and arrange strips on top of halibut. Sauté onions in bacon drippings and spread over top of halibut and bacon. Mix sour cream, lemon juice, mayo, salt, pepper, and garlic powder.  Spread mixture over the fish, covering it completely.  Top the casserole dish with cheddar, cover with foil, and bake at 350 degrees for 30 mins. Remove foil and bake for 10 mins more.  Great for family or company!