Cook artichoke hearts as directed on package. Place in a flat, buttered casserole. Cover with sauteed mushrooms. Cook oysters in their liquid until edges begin to curl. Drain thoroughly in colander, reserving liquid. Melt butter and saute onion until tender; add parsley and cook a minute. Add flour, stirring until smooth. Add enough white wine to oyster liquid to make 1 1/2 cups. Add seasonings and stir constantly until thick. Add oysters and spoon mixture over artichokes and mushrooms. Arrange lemon slices over top; add a dash or two of paprika and bake at 350 degrees about 10 minutes or until bubbling.