In a small bowl, whisk together tamari, rice vinegar, water, sriracha, honey, cornstarch and garlic. Set aside.
Heat ½ tablespoon oil in a large saute pan over medium heat. Add the quartered mushrooms and cook until browned and softened, about 5 minutes.
Remove mushrooms from pan, add another ½ tablespoon oil and the chopped zucchini. Saute until browned and softened for 5-7 minutes.
Remove zucchini from the pan. Add the remaining 1 tablespoon of oil along with the chicken. Brown on both sides until fully cooked through, about 8-10 minutes.
Once the chicken is cooked, add the zucchini and mushrooms back into the pan and lightly season with salt and pepper. Add the sauce and bring to a simmer. Cook until the sauce has thickened.
Turn off the heat and stir in the sesame oil. Top with sesame seeds and green onion. Serve with rice.