Combine all of the Meatball ingredients in medium mixing bowl and mix thoroughly (using your hands is usually the easiest).
Take a heaping tablespoon of the ground beef mixture and use your hands to roll it into a meatball. Continue until all the meat is used (you should have around 20 meatballs).
Place meatballs in medium-sized casserole dish, approximately 1/2 - 1 inch apart.
Sprinkle the tops lightly with salt and pepper and cover with marinara sauce.
Cook for 25 minutes or until cooked through.
Add spaghetti squash and stir to loosely combine.
Sprinkle with nutritional yeast (optional).
Place back in the oven for 10-15 minutes.
Remove from oven and serve immediately.
Notes
This is an easy meal to meal-prep: simply make the meatballs ahead of time (you could even just bake them without the sauce if you wanted) then place them in a casserole dish, along with the sauce (if you haven't used it already) and reheat in the oven at 350 for 15-20 minutes (or until heated through). Then add the spaghetti squash for another 10 minutes.