Lighter Fresh Tomato Quiche
["3 medium fresh tomatoes (about 1 lb.)", "1 Tbsp. margarine", "1 1/2 c. sliced mushrooms", "1/2 c. chopped onion", "1 1/2 c. plain unseasoned croutons", "1 1/4 c. low-fat milk", "2 eggs", "1/2 c. grated Parmesan cheese", "1/4 tsp. salt", "1/8 tsp. ground black pepper"]
["Preheat oven to 375\u00b0.", "Use tomatoes held at room temperature until fully ripe; cut 1 tomato into 1/4-inch thick slices for garnish; set aside."]
["tomatoes", "margarine", "mushrooms", "onion", "croutons", "low-fat milk", "eggs", "Parmesan cheese", "salt", "ground black pepper"]