Cook mushrooms in 1 tablespoon butter until tender. Remove from pan and set aside. In the same pan, melt the remaining 3 tablespoons butter. Blend in flour, salt and pepper; add cream, sherry, cheese and bacon bits. Cook until thick, stirring constantly. Add mushrooms and artichokes. Set aside and keep warm. Cut fish into serving-size portions. Brush fish with lemon juice and grill over medium-hot coals or gas elements until fish flakes easily. Serve fillets with warm sauce.