Whisk together rice vinegar, lime zest, fish sauce, ginger, Thai chili garlic sauce and honey in small bowl. Reserve ⅓ cup (75 mL) mixture (cover and keep chilled if marinating chicken overnight). Pour remaining marinade into large zip-top bag. Add chicken and turn to coat. Seal bag and marinate in refrigerator 30 min., or up to 8 hr.
Remove chicken from bag (discard marinade). Place chicken on grill preheated to medium-high. Grill 5 to 6 min. per side, or until instant-read thermometer registers 165˚F (74˚C) in thickest part of thigh. Remove from grill; let rest 5 min. Use two forks or hands to shred chicken into large bowl. Stir in spinach, mango and cilantro. Set aside.
Bring reserved ⅓ cup (75 mL) marinade to a boil in small saucepan over medium-high heat. Simmer until slightly thickened, about 1 min. Cool until warm. Pour over shredded chicken mixture; toss to combine.
Toast buns on grill. Tuck chicken mixture, tomato and cilantro garnish into buns. Serve with lime wedges.
Thai chili garlic sauce can be replaced with 1 tsp (5 mL) hot pepper flakes. Instead of filling for sandwiches, shredded chicken mixture can be served on top of a green salad.