In a medium-sized bowl, combine 1 Tbsp. chicken broth, 1 Tbsp. soy sauce, 2 tsp. sesame oil and 1 Tbsp. cornstarch/water mixture and mix together. Add chicken pieces to mixture. Toss to coat. Cover bowl and place in refrigerator for about 30 minutes.
Heat vegetable oil in a large skillet. Add zucchini and peppers and saute for a minute or so (don't let them get too soft or they will become soggy). Add garlic and saute another minute. In a small bowl, combine remaining broth, soy sauce, oil and cornstarch/water mixture. Stir in chili paste, vinegar and sugar. Add sauce mixture to skillet with the sauteed veggies. Add green onion, water chestnuts, peanuts, and red pepper flakes. Heat sauce slowly over medium heat.
Remove chicken from marinade and saute in a medium skillet until meat is white and juices run clear. Add sauteed chicken to sauce and simmer together until sauce thickens. If the sauce is too thick, add a little bit of chicken broth a little at a time until sauce reaches desired thickness.