Heat oven to 375 degrees.
For meatballs: Using hands, combine ground turkey, green onions, sesame oil, red pepper flakes, salt, pepper, garlic and powdered ginger. In food processor, pulse pecans until coarsely ground to similar consistency as panko bread crumbs. Scoop 1 tablespoon meat mixture at a time and roll into meatballs. Roll meatballs in ground pecans until evenly coated. Place pecan-crusted meatballs on parchment-lined baking sheet; bake approximately 20 minutes. Flip after 15 minutes.
For sauce: In small saucepan over medium heat, combine soy sauce, cornstarch, fish sauce and sesame oil. Stir until sauce thickens, about 3 minutes. Remove from heat and let cool.
Sprinkle lettuce cups with shredded carrots. Place meatballs on top and drizzle with sauce. Garnish with scallions and cilantro, if desired.