Place chicken in a food processor; pulse until coarsely ground.
Heat a large nonstick skillet over medium heat. Add chicken, broth, and ginger to pan; cook 8 minutes or until chicken is done, stirring frequently. Drain well, and transfer to a large bowl. Add water chestnuts, red onion, green onions, cilantro, juice, sugar, fish sauce, and salt to bowl; toss well. Place 1/3 cup chicken mixture into each lettuce leaf. Serve with peanuts and serrano.