Preheat the oven to 375 degrees F. Combine meatball ingredients in a bowl. Roll into 1-inch round balls and place on a non-stick or parchment-lined baking tray. Bake 20-25 minutes, or until cooked through. Make the sauce by heating the oil in a wok or large skillet over medium-high. Add the onion and bell peppers and cook 3 to 4 minutes. Add all remaining sauce ingredients, except cornstarch mixture, and gently simmer 5 mins.
Thicken the sauce with the cornstarch mixture. Drain the meatballs well, place them in the sauce, turn to coat, and then serve.