In a medium skillet, heat 2 tablespoons olive oil over medium heat. Add the onion and garlic and cook until softened, about 7 minutes. Let cool.
In a large bowl, combine the lamb, bread, egg, lemon peel, chopped mint, coriander, cumin, cinnamon, nutmeg and cooked onion mixture; season with salt and pepper. Shape into 20 meatballs and dust with flour.
In a large skillet, heat the remaining 1/4 cup olive oil over medium heat. Working in batches, fry the meatballs until golden-brown, 8 to 10 minutes. Drain on paper towels.
Serve the meatballs with the mint leaves, lemon wedges and yogurt.