Slice the chicken breasts into strips. Whisk together the soy sauce, sugar, cornstarch, minced garlic, ginger and sesame oil until the cornstarch has dissolved. Mix-in the sliced green onion.
Place into a plastic storage bag, pour the marinade over chicken. Marinate for at least 4 hours or overnight.
To stir-fry: Heat a few drizzles of vegetable or peanut oil in a hot skillet, around 3 Tbsp. Add the broccoli florets, green onion, ginger, minced garlic, 3 Tbsp water, and a sprinkle of salt and black pepper to your taste.
Cook for 3 minutes or until crisp tender and bright green in color. Remove to a plate.
Heat the remaining 3 Tbsp of oil. Remove chicken from marinade and add to hot skillet.
Add 1 tsp red pepper flakes to the chicken. Stir fry for 3-4 minutes until the chicken has browned and cooked through. Add the broccoli back to the skillet.
Drizzle with the ¼ cup hoison sauce, more if desired, continuing to saute 1-2 minutes until heated thru.
Serve immediately over rice.