Preheat oven to 350° F.
Sauté mushrooms, onion and garlic in olive oil in a large skillet until tender, 8 to 10 minutes. Stir in flour; cook 1 to 2 minutes longer.
Combine mushroom mixture and remaining ingredients, except parsley, in 2-quart casserole.
Bake, uncovered, at 350° For 45 minutes; sprinkle with parsley before serving, if desired.
Servings: 6