Melt 1/4 cup butter. Reduce to low: add crabmeat and shrimp, coating well.
Stir in flour. Pour in the stock, cream and wine, stirring until blended, Heat gently until hot.
Stir in mushrooms, green pepper, rice salt and pepper.
Remove from heat; spoon into pocket of the halibut. Spread the excess mixture over the bottom of baking dish which has been lightly greased.
Arrange the stuffed fish on top and pour over the melted butter. Bake in preheated 350F oven, covered, for 50 minutes or until fish is tender but still firm.
Remove from oven. Garnish with parsley and lemon wedges and serve at once.