Saute green onions, butter and garlic. Stir in flour. Cook over low heat until bubbly. Combine oyster liquid, mushroom liquid and enough heavy cream to make a total of 1 1/2 cups of liquid. Add to sauce mixture slowly and cook until sauce is smooth and creamy. Add lemon juice, wine, mushrooms, parsley and seasonings to taste. Simmer mixture on low heat for 15 minutes. Place 1 to 2 inch rock salt in a large Pyrex baking dust. Place oyster shells onto this bed of salt. Place 1 oyster in each half shell and bake at 375 degrees until edges of the oysters curl. Drain any liquid from individual oysters with meat basting bulb. Top oysters with sauce, and sprinkle with grated fresh parmesan cheese. Return to oven and broil until slightly brown. Serve with lemon wedges and toast points.