In a large mixing bowl, combine the ground turkey, breadcrumbs, egg, minced garlic, chopped onion, parsley, oregano, cumin, salt, and black pepper. Mix with clean hands until just incorporated, about 30 to 45 seconds. Avoid overmixing to prevent tough meatballs.

Roll the mixture into uniform meatballs about 1 to 1.5 inches in diameter. You should get approximately 16 to 18 meatballs. Wet your hands slightly to prevent sticking while rolling.

For oven-baking: Preheat oven to 400°F (200°C). Place meatballs on a parchment-lined baking sheet with 1 inch of space between each. Bake for 15 to 20 minutes until golden brown with slightly crispy edges and internal temperature reaches 165°F (74°C).

For pan-frying: Heat a drizzle of olive oil in a large 12-inch skillet over medium heat. Cook meatballs for 4 to 5 minutes per side, turning carefully to brown all sides until fully cooked through (8 to 10 minutes total).

For air-frying: Cook at 380°F (193°C) for 10 to 12 minutes, turning halfway through until internal temperature reaches 165°F.

While the meatballs cook, prepare the tzatziki. Grate the cucumber using a box grater, then squeeze out excess moisture using paper towels or cheesecloth to prevent watery sauce.

In a mixing bowl, combine Greek yogurt, drained cucumber, minced garlic, lemon juice, fresh dill, and olive oil. Stir until smooth and evenly mixed.

Taste the tzatziki and adjust seasoning with salt, pepper, and additional lemon juice if desired. Refrigerate for at least 30 minutes to let the flavors meld together.

Serve the warm meatballs with a generous dollop of chilled tzatziki sauce. Enjoy with pita bread, rice, or a fresh Greek salad for a complete meal.