In a small bowl, stir together soy sauce, vinegar, sugar, fish sauce, sriracha and 1 tablespoon water. Set aside.
Heat oil in a large nonstick skillet over medium-high heat. Crumble in chicken and cook 2 minutes, breaking up large pieces with a wooden spoon. Stir in red pepper, sugar, garlic powder, ginger and sriracha. Cook 3 minutes, until no longer pink, stirring occasionally. Take off heat and stir in scallions and soy sauce.
To serve, spoon 1/4 cup chicken mixture into each lettuce leaf and top with cucumber, scallions, mint and a squeeze of lime. Serve with Dipping Sauce and brown rice.