Combine chicken, 2 teaspoons lemon juice, and soy sauce in a large zip-top plastic bag; seal and marinate in refrigerator for 10 minutes, turning bag once. Remove chicken from bag. Place chicken on a broiler pan coated with cooking spray; broil 6 minutes on each side or until done. Cool; shred chicken with 2 forks.
Combine chicken, 1 teaspoon lemon juice, mayonnaise, and next 5 ingredients (mayonnaise through pepper). Spread 1 cup chicken mixture over each of 2 bread slices. Top each with 1 lettuce leaf, 2 tomato slices, and 1 bread slice. Store sandwiches in small zip-top bags in refrigerator.