Combine first 6 ingredients in a large zip-top plastic bag. Place 2 tablespoons soy sauce mixture in a small bowl; set aside. Add chicken slices to remaining soy sauce mixture in bag; seal. Refrigerate 2 hours. Cook rice according to package directions. Remove chicken from bag; discard marinade. Heat a large skillet over medium-high heat. Add oil to pan; swirl to coat. Add chicken; cook 2 minutes on each side or until done. Sprinkle sesame seeds over chicken. Place 3 tablespoons rice in each lettuce leaf; top each lettuce leaf with 1/3 cup chicken mixture, 2 cucumber slices, and about 1 1/2 teaspoons green onions. Serve with reserved 2 tablespoons soy sauce mixture.