Make the tzatziki: In a bowl, combine yogurt, cucumber, garlic, dill, lemon juice, salt, and pepper. Mix well and refrigerate until ready to serve.
Prepare meatballs: In a large mixing bowl, combine turkey, breadcrumbs, egg, garlic, red onion, oregano, cumin, parsley, salt, pepper, and lemon zest. Mix until just combined—do not overwork.
Shape and cook: Roll mixture into 1 to 1.5-inch meatballs. Heat olive oil in a large skillet over medium heat. Add meatballs and cook, turning occasionally, until browned on all sides and cooked through, about 10–12 minutes.
Serve: Serve warm with a side of tzatziki. Optional: serve over rice, in a pita, or alongside a Greek salad.