In a medium bowl, beat egg lightly; mix in onion, crumbs, oregano, garlic, salt & pepper. Mix in chicken or turkey. Scoop heaping tablespoonfuls into balls.
In large skillet, heat oil over medium heat; cook meatballs, covered, for 8-10 minutes or until browned on all sides. Transfer to paper towel-lined plate.
Pasta & Sauce
Add garlic, mushrooms, onion, green pepper, basil, sugar, oregano, salt, pepper and 2 tbsp water to skillet; cook over medium heat, stirring occasionally, for about 10 minutes or until vegetables are softened.
Stir in diced tomatoes & tomato paste; bring to a boil. Add meatballs; reduce heat & simmer for 30 minutes or until slightly thickened.
Meanwhile, in large pot of boiling, salted water, cook rigatoni for about 3 minutes or until el dente. Drain & return to pot; add tomato sauce, stirring to coat NUDLs.