Preheat the oven to 375 and spray a 2 qt. baking dish with cooking oil.
Make the sauce:
Heat a large skillet over medium heat, and add the oil. Stir in the onion and cook, stirring frequently, until tender, 5-7 minutes. Add the garlic and cook until fragrant, 30-60 seconds. Add the balsamic vinegar, scraping anything off the bottom of the pan, and cook until it’s almost fully absorbed.
Add the tomato sauce, red pepper flakes, basil, ,oregano, and salt and pepper to taste. Bring to a low boil, and then simmer while you prepare the rest of the meal.
In a large bowl, combine the quinoa and chicken with the sauce and mix thoroughly.
Place the mixture in the baking dish, and sprinkle with the mozzarella cheese and the Parmesan. Add the breadcrumbs, if using.
Cover with foil and bake for about 15 minutes. Remove foil and continue to bake until cheese is lightly browned and bubbly, about 10 more minutes.
Sprinkle with parsley (and additional Parmesan) before serving, if desired.