For the dressing: In a small bowl, whisk together fish sauce, vinegar, sesame oil, and pepper flakes; set aside at room temperature.
For the meatballs: In a large bowl, stir together turkey, garlic, ginger, sesame oil, vinegar and soy sauce. Form mixture into 24 (2-inch) meatballs.
Lightly coat a large nonstick skillet with cooking spray and heat to medium-high. Add meatballs in two batches and cook, turning occasionally, until browned on all sides, 5 to 7 minutes for each batch.
Lay 3 lettuce leaves on each of 4 plates. Place 2 meatballs on top of each leaf. Top meatballs with cucumber and mint leaves, drizzle with dressing and serve.
Per serving: 180 calories, 6 g fat, 0.5 g saturated fat, 30 g protein, 4 g carbohydrates, 0 g fiber, 480 mg sodium.