Prepare pasta according to package directions. While pasta is cooking, toss chicken with salt, pepper and garlic. Coat a large non-stick skillet with cooking spray; place over medium-high heat until hot. Add chicken mixture; stir-fry 4 to 5 minutes or until chicken is cooked through. Remove chicken from skillet and place in a medium bowl. Add broccoli, red pepper and chicken broth to skillet. Cover; simmer over medium heat 5 to 6 minutes or until vegetables are tender-crisp. Transfer to bowl with chicken. In a small bowl, combine 1/4 cup of the milk with cornstarch, mixing until smooth. Add to skillet with remaining milk; bring to a boil, stirring constantly. Reduce heat; stir in mustard. Stir in reserved chicken mixture. When pasta is done, drain well. Toss with chicken mixture. Serve immediately with additional freshly ground pepper, if desired.