Preheat oven to 350 degrees F. Thoroughly coat a large baking sheet with cooking spray.
In a large bowl, combine ground chicken, cooked quinoa, chopped onion, garlic, zucchini, egg, parsley, red pepper flakes, oregano, salt and ground pepper.
Mix until evenly distributed. Using a one tablespoon portion of the chicken mixture, form meatballs by rolling between the palms of your hands. Place the meatballs on the prepared baking sheet, spacing them apart evenly.
Bake until the meatballs are firm to the touch and cooked through, approximately 20 minutes.
While the meatballs are cooking, heat the tomato sauce in a large saucepan set over medium heat.
Transfer the meatballs to the tomato sauce and gently stir to coat the meatballs.
Serve over spaghetti squash, zucchini noodles or whole-grain pasta!