Coat a medium nonstick skillet with cooking spray; add oil. Place over medium-high heat until hot. Add chicken, and cook 5 minutes, stirring frequently. Remove from skillet, and keep warm. Wipe drippings from skillet with a paper towel.
Coat skillet with cooking spray. Add yellow squash and zucchini; saute 7 minutes. Stir in onion and red pepper; saute 1 minute. Add chicken, chicken broth, and soy sauce. Cook 3 minutes, stirring frequently. Sprinkle with sesame seeds.