Marinate the chicken in the garlic, ginger, gluten-free soy sauce, and apple cider vinegar in a bowl or ziplock and refrigerate for at least 30 minutes.
Heat the olive oil in a large wok and cook the onions for two minutes then add the broccoli and bell peppers and cook for a few more minutes until crisp-tender, then remove the vegetables from the wok and add to a bowl with a foil cover to keep warm.
Drain the chicken from the marinade (keep the marinade, we will cook it later) and add a little more oil to your wok and cook the chicken over high heat for 3-4 minutes per side or until chicken pieces are fully cooked.
Return the cooked vegetables to the wok along with the remaining stir fry marinade, mushrooms, sesame oil, and red pepper flakes and cook for about three to four more minutes until the mushrooms are cooked.
Serve hot.
