First, marinate the steak. Combine soy, baking powder, ½ tsp salt, ½ tsp pepper, ½ tsp red pepper flakes, ginger, and garlic and pour into a ziplock with steak.
Marinate steak for 1 hour.
Preheat a frying pan over high heat
Prepare teriyaki sauce. Mix water and cornstarch until dissolved. Combine cornstarch mixture and all remaining ingredients into a saucepan over medium heat. Cook until thickened, about 10 minutes.
Meanwhile, remove steak from the marinade and pat dry. Season lightly with remaining pinch of salt, pepper, and red pepper flakes.
Sear steak for 2 minutes per side. Set aside on a wooden cutting board.
Slice bell pepper and onions into quarters. Sear for 2 minutes. Remove and set aside.
Lower the heat to medium/low
Cut the steak, onions, and peppers into bite sized pieces
Add back to the pan and pour in the Teriyaki sauce. Toss to coat.
Cover and simmer for 3-5 minutes.
Garnish with chopped green onions and Enjoy!