Combine together chicken and cornstarch (corn flour) in a large bowl. Season with salt and pepper.
Meanwhile, heat oil in a wok over high heat.
Add chicken. Stir and cook chicken for about 5-7 minutes or until meat is no longer pink in the center and cooked through.
Move chicken to the side.
Add garlic and red pepper (chili) flakes. Stir fry for a few seconds.
Add vegetables. Stir fry vegetables with chicken for about 3 minutes or until just tender.
Add teriyaki sauce and soy sauce. Cook, stirring, for about 2 minutes.
Sprinkle with spring onions (scallions).
Divide stir fry among serving bowls.
Garnish with green chilies, coriander (cilantro) leaves and sesame seeds.
Serve with noodles or rice.