In a large skillet, cook chicken over medium heat until no longer pink, 8-10 minutes, breaking it into crumbles; drain. In the same skillet, heat oil over medium heat. Add shallots and chiles; cook and stir until tender, 3-4 minutes. Add garlic; cook 1 minute longer. Stir in the cooked chicken, lime juice, fish sauce, chili sauce, brown sugar and Sriracha. Cook and stir until heated through. Stir in cilantro and mint. Serve with rice and, if desired, lettuce leaves.