Preheat the oven to 375°F (190°C).
In a large mixing bowl, combine ground turkey, breadcrumbs, onion, parsley, garlic, oregano, cumin, salt, and pepper.
Mix the ingredients gently but thoroughly using your hands or a spatula.
Shape the mixture into 1- to 1.5-inch meatballs and place them on a baking sheet.
Bake the meatballs for 25-30 minutes or until cooked through.
While the meatballs bake, prepare the tzatziki sauce.
In a bowl, combine Greek yogurt, grated cucumber, lemon juice, dill, and a pinch of salt.
Stir well until the mixture is smooth and creamy, then chill in the refrigerator until serving.
Serve the meatballs warm with tzatziki on the side.