1. Preheat grill to medium-high heat (350° to 400°).
2. Combine first 14 ingredients in a large mixing bowl, stirring until well blended. Divide mixture into 16 portions; shape each portion into a cylinder. Brush each meatball evenly with olive oil.
3. Grill meatballs, turning once, 6 to 10 minutes or until cooked through. Serve with Avocado-Mint Tzatziki and flatbread.