To prepare chicken, combine first 6 ingredients in a large zip-top plastic bag. Add chicken; seal and marinate in refrigerator 15 minutes, turning bag occasionally. Remove chicken from bag; discard marinade.
Thread chicken pieces onto 6 (8-inch) skewers. Place skewers on grill rack coated with cooking spray; grill 8 minutes or until chicken is done, turning frequently.
To prepare mint sauce, place bread slices in a food processor, and pulse until coarsely crumbled. Add mint, olive oil, white wine vinegar, 1/2 teaspoon salt, and 2 garlic cloves; pulse until combined. With processor on, slowly pour water through food chute, and process until smooth and well blended.