Preheat oven to 350 degrees. Spray medium skillet with nonstick cooking spray. Add mushrooms, green onion and garlic. Cook and stir over medium heat until mushrooms are softened. Add spinach and water. Cover; cook until spinach is wilted, about 3 minutes. Combine ricotta cheese, milk, egg, nutmeg, and pepper in large bowl. Gently stir in noodles and vegetables; toss to coat evenly. Lightly coat shallow 1 1/2 quart casserole with nonstick cooking spray. Spread noodle mixture in casserole. Sprinkle with Swiss cheese. Bake 25 to 30 minutes or until knife inserted halfway to center comes out clean. Makes 6 (1 cup) servings.