Prepare the Steak: In a large bowl, toss the steak bites with the cornstarch, garlic powder, garlic salt, and red pepper flakes until well coated.

Make the Teriyaki Sauce: In a small bowl, mix together the teriyaki sauce, brown sugar, and sesame oil. Set aside for later use.

Sear the Steak Bites: In a large skillet or wok, heat 1 tablespoon of olive oil over medium-high heat. Once hot, add the steak bites in a single layer, working in batches if necessary to avoid overcrowding. Cook the steak for 2 to 3 minutes on each side, or until it develops a rich brown crust and reaches your preferred doneness. Once cooked, transfer the steak bites from the skillet and set them aside.

Cook the Vegetables: Add a bit more olive oil to the skillet if needed. Add the sliced green bell pepper (or poblano) and onion. Cook for about 3-4 minutes, stirring frequently, until the vegetables are tender-crisp.

Combine and Glaze: Return the steak bites to the skillet, along with the prepared teriyaki sauce. Toss everything together until the steak and vegetables are evenly coated with the sauce.

Serve: Transfer the teriyaki steak bites and vegetables to a serving platter. Serve hot, garnished with extra red pepper flakes or sesame seeds if desired. Pair with rice or noodles for a complete meal.