For sauce, in a medium saucepan cook onion and garlic in hot butter until onion is tender. Carefully stir in the undrained tomatoes, sugar, salt, and pepper.
Bring to boiling; reduce heat. Simmer, uncovered, for 10 minutes or to desired consistency, stirring occasionally. Stir in basil. Keep warm.
Meanwhile, with a meat mallet, pound each chicken breast half between two pieces of plastic wrap to 1/4-inch thickness.
In a shallow dish stir together bread crumbs, the 3 tablespoons Parmesan cheese, and oregano. In another bowl stir together the egg and milk. Dip chicken breast halves in egg mixture, then in crumb mixture to coat. Spray both sides of each chicken half with olive oil spray and bake at 425 degrees for 15 to 25 minutes (adjust according to the thickness of the chicken) until cooked through. Transfer chicken to a serving platter.
Spray both sides of each chicken half with olive oil spray and bake at 425 degrees for 15 to 25 minutes (adjust according to the thickness of the chicken) until cooked through. Transfer chicken to a serving platter.
To bake the spaghetti squash, cut squash in half lengthwise. Remove seeds. Place in a baking dish with the cut sides down. Bake at 350 degrees for 45 to 50 minutes or until squash is tender.
Place chicken on bed of spaghetti squash. Spoon sauce over chicken. Top with shredded mozzarella and 1 tablespoon Parmesan cheese. Let stand about 2 minutes or until cheese melts.