Cook spaghetti according to package directions. Drain; keep warm.

Lightly coat a 3-quart baking dish with cooking spray. Set aside.

In large saucepan, heat olive oil over medium heat. Add onion. Cook and stir over medium heat for 5 minutes or until tender. Add mushrooms, zucchini, sweet pepper, and garlic. Cook and stir for 3 minutes more or till vegetables are just tender. Drain off liquid; discard. Stir salt, oregano, and pepper into vegetable mixture. Set aside to cool.

In large mixing bowl, beat eggs, milk and Parmesan with an electric mixer on low speed till combined. Add cream cheese pieces. Beat for 30 seconds.

Place cooked spaghetti onto bottom of prepared baking dish. Add vegetables. Sprinkle with cheddar cheese. Pour egg mixture evenly over mixture in dish. Pat down with a spatula or back of a spoon so most of solids are covered with the liquid.

Bake, uncovered, in a 350 degree F oven about 40 minutes or till set and lightly brown on edges. Cut into serving-size pieces. To serve, spoon about 1/3 cup of Sauteed Tomato Sauce on each plate; place a frittata serving on top of sauce. Serve immediately. Makes 12 servings.

In a medium saucepan, melt 2 tablespoons butter or margarine over medium heat. Cook 3/4 cup chopped onion in hot butter for 5 minutes or till onion is tender, stirring often. Add 2 cloves minced garlic; cook and stir 30 seconds more. Carefully stir in 1, 28-ounce can whole Italian-style tomatoes in puree, undrained and cut up; half of a 6-ounce can (1/3 cup) tomato paste; 1/2 teaspoon sugar; 1/2 teaspoon kosher or sea salt; and 1/4 teaspoon freshly ground black pepper. Bring to boiling; reduce heat. Simmer, uncovered, about 15 minutes or to desired consistency. Stir in 1 teaspoon dried oregano, crushed. Cook for 5 minutes more. Makes about 4 cups.