01 - Grate the cucumber and squeeze out all excess moisture using a clean kitchen towel or cheesecloth. In a medium bowl, combine the drained cucumber with Greek yogurt, minced garlic, chopped dill, mint (if using), olive oil, lemon juice, salt, and pepper. Stir until well incorporated, then refrigerate for at least 20 minutes to allow the flavors to meld.
02 - In a large mixing bowl, combine the ground turkey, grated onion, minced garlic, breadcrumbs, egg, chopped parsley, chopped dill, dried oregano, ground cumin, lemon zest, salt, and black pepper. Gently mix with your hands until just combined, being careful not to overwork the mixture.
03 - Using approximately 1 tablespoon of mixture per meatball, roll into uniform balls. You should get 20 to 24 small meatballs. Arrange them on a plate or parchment-lined tray as you work.
04 - For pan-frying: heat olive oil in a large skillet over medium heat. Add the meatballs in batches without crowding the pan. Cook for 8 to 10 minutes, turning every couple of minutes to brown evenly on all sides, until cooked through to an internal temperature of 165°F. For baking: preheat the oven to 400°F. Arrange the meatballs on a greased baking sheet, drizzle with olive oil, and bake for 18 to 20 minutes until golden brown and fully cooked.
05 - Arrange the hot meatballs on a serving platter alongside the chilled tzatziki sauce. Garnish with lemon wedges and fresh herbs. Serve with warm pita bread or a crisp side salad if desired.