Heat a large non-stick skillet to medium-high then add oil. Add steak, ginger, coriander, salt and pepper then stir to combine. Cook for 3-5 minutes or until steak is browned but still pink in the middle. Remove steak, place on a plate then set aside.
Add bell peppers and onion to skillet then cook until softened, about 5 minutes.
While vegetables are cooking make sauce by adding teriyaki, soy sauce, brown sugar, sesame oil, sriracha, and cornstarch to a bowl. Whisk until no lumps of cornstarch remain.
When vegetables are softened, add garlic, stir to combine then continue cooking for 2 minutes. Add steak back to skillet.
Add sauce, stir to combine with steak and vegetables, bring to a slight boil, then reduce heat. Sauce should thicken within a couple of minutes.
Serve over rice and garnish with sesame seeds.