Preheat the oven to 375F if you choose to bake the meatballs.
Heat olive oil in a saute pan on medium-high heat, then add the onions. Cook for 6 minutes until translucent and soft. Add garlic and cook for another minute. Set aside. Allow to slightly cool.
In a mixing bowl, combine ground turkey, salt, pepper, garlic powder, onion powder, oregano, parsley, egg, and breadcrumbs. (*1) Add the onions and garlic, then mix to combine into the meat. Mix just until combined (over mixing will create tough meatballs).
Take approximately 3 tablespoons of the meat mixture and roll it into a ball. Press a cube of cheese into the ball of meat, making sure that the meat completely surrounds the cheese. Set aside the meatball on a plate and repeat with the remaining meat and cheese.
In that same saute pan you used for the onions and garlic, heat 2 tbsp olive oil on medium-high heat. Place a few meatballs at a time and brown on both sides, about 5 minutes each. Place meatballs on a sheet pan with aluminum foil and sprayed with cooking spray. Repeat with the remaining meatballs.
If you are baking the meatballs, bake the meatballs in a 350F oven for 20 minutes until the internal temperature reaches 165F.
If you are using the tomato sauce, heat the sauce in a saucepot and place the meatballs in the sauce for an additional 20 minutes so it will flavor up the sauce.