In a large mixing bowl, combine the minced beef, finely chopped small onion, egg, milk, your choice of gluten-free binder, salt, pepper, oregano, and dried parsley. Use your hands to mix everything together until well combined but be careful not to overmix, as this can make the meatballs tough.
Once your mixture is ready, take a handful and form small meatballs, about the size of a golf ball. Place them on a baking sheet lined with parchment paper, ensuring they are spaced apart to allow even cooking.
Preheat your oven to 200°C (400°F). Bake the meatballs for about 20-25 minutes, or until they are golden brown and cooked through. You can check their doneness using a meat thermometer; the internal temperature should reach 70°C (160°F).
While the meatballs are baking, heat the olive oil in a large skillet over medium heat. Add the chopped onion and minced garlic, sautéing until the onion is translucent and fragrant. Stir in the chopped tomatoes, balsamic vinegar, and the mixed Italian herbs. Season with salt and pepper to taste. Let the sauce simmer for about 10-15 minutes to allow the flavors to meld.
In a large pot, bring water to a boil and cook the gluten-free spaghetti according to package instructions. Be sure to stir occasionally to prevent sticking. Drain and set aside once cooked.
Once the meatballs are done, gently add them to the simmering sauce, ensuring they are coated well. Serve the meatballs and sauce over a bed of gluten-free spaghetti. If desired, sprinkle with freshly grated parmesan cheese for an extra touch of flavor.