Rinse rice and cook in chicken broth with 1 tablespoon olive oil and lemon juice until liquid is absorbed.
Preheat oven to 200C (400F) and line a baking sheet with parchment paper.
In a large bowl, combine ground beef, lamb, diced red onion, 2 cloves minced garlic, breadcrumbs, egg, oregano, mint, salt, and pepper.
Form meat mixture into 24 small meatballs and arrange on the prepared baking sheet.
Bake meatballs for 18 to 20 minutes until browned and cooked to an internal temperature of 71C (160F).
Prepare tzatziki by combining grated cucumber, Greek yogurt, remaining minced garlic, 1 tablespoon olive oil, and 1 tablespoon lemon juice in a small bowl.
Dice remaining cucumber and halve cherry tomatoes to prepare the fresh salad components.
Assemble bowls by placing a portion of lemon rice at the base, followed by 6 meatballs, fresh vegetables, olives, and crumbled feta.
Top each bowl with a generous portion of tzatziki sauce and garnish with extra mint if desired.