Cut 1 orange into wedges (peel intact); set aside. Of the remaining 2 oranges, remove zest of 1 and juice of both; place zest and juice in a glass bowl. Add lemon juice, vinegar, pepper and mustard; whisk. slowly whisk in sesame oil; set aside.
Place chicken between two sheets of plastic wrap; pound with a meat tenderizer to 1/2 inch thick. Place chicken in a glass bowl; pour half reserved vinegar mixture over chicken. Coat thoroughly, cover with plastic wrap, and chill 1 to 2 hours.
Heat grill or grill pan until very hot. Coat asparagus and zucchini with olive oil; sprinkle with 1/2 tsp. salt. Grill vegetables and reserved orange wedges until tender. Remove chicken from marinade; season with remaining tsp. salt; discard marinade, Grill until browned on both sides and cooked through. Arrange chicken and vegetables on platter; sprinkle with the sesame seeds. Serve with remaining vinegar mixture.