CUT chicken into 1-oz. strips; place in large bowl. Add mustard; toss to evenly coat.
MIX tempura mix and ice water until well blended.
DIP chicken in flour, then in tempura batter. Roll in pretzel crumbs to evenly coat all sides of chicken. Place in single layer in sheet pans; cover. Refrigerate until ready to serve.
FOR each serving: Deep-fry 3 oz. chicken in hot oil (325°F) for 3 to 4 minutes or until chicken is cooked through (170°F). Serve immediately.