Preheat a non-stick skillet over medium heat and add the olive oil.
Finely mince the garlic and quartered onion, then sauté them in the skillet until softened and fragrant.
In a bowl, combine the lean ground turkey with the egg white, sautéed garlic and onion, and grated Parmesan cheese. Season lightly with salt and pepper.
Form the mixture into small meatballs, approximately 1.5 inches in diameter.
Lightly sauté the meatballs in the skillet until they are browned on all sides and cooked through, about 8-10 minutes. Alternatively, you can bake them at 400°F for 12-15 minutes.
Using a spiralizer or vegetable peeler, create zucchini noodles from the medium zucchini.
Warm the tomato sauce in a small pan, then pour it over the zucchini noodles arranged on a plate.
Top the zucchini noodles with the turkey meatballs, sprinkle with extra Parmesan if desired, and serve immediately.