Place halibut in baking dish, sprinkle with old bay & lemon juice. Dot with slices of butter. Bake at 350 until halibut flakes with a fork. Cool slightly and flake into bite sized pieces.
Mix mayo, sour cream & cream cheese in large bowl till blended. Carefully stir in halibut, green chilis, onion & parsley. Add salt & pepper to taste.
Place filling in tortillas & roll up. Place seam side down in 15x9 baking dish, greased. Pour heavy cream over top, using as much as needed to cover. Top with cheeses. Bake at 350 for 45 mins. Do not over bake as it will dry out.