MIX mustard, honey, lime juice and garlic powder until well blended. Reserve 3 cups of the mustard mixture (or 2 Tbsp. for trial recipe) in separate container for assembly and serving of the sandwiches.
GRILL or broil chicken breasts 8 to 10 minutes or until cooked through (165°F),turning after 4 minutes and brushing generously with remaining mustard mixture during cooking time. Discard any remaining mustard mixture. Cut each chicken breast horizontally in half.
FOR each serving: Spread bottom half of roll with 1 Tbsp. of the reserved mustard mixture; cover with split chicken breast, 1 lettuce leaf, 2 tomato slices and top of roll spread with additional 1 Tbsp. of the reserved mustard mixture.
SERVE with a (1-oz.) portion cup filled with reserved mustard mixture on the side.