In a medium bowl, whisk together soy sauce, minced garlic, minced ginger, and brown sugar until well combined. Add the thinly sliced steak, ensuring it’s fully coated with the marinade. Cover the bowl and let the steak marinate for at least 15 minutes at room temperature.

Place a large skillet or wok on the stove over medium-high heat. Add a tablespoon of oil and allow it to heat until shimmering.

Remove the steak from the marinade, reserving the marinade for later. Working in batches, add the steak strips to the hot skillet. Cook for 1-2 minutes per side until browned. Transfer cooked steak to a plate and cover loosely with foil.

In the same skillet, add more oil if needed, and toss in the bell peppers and sliced onion. Stir-fry for 3-5 minutes, or until tender-crisp.

Mix cornstarch with a tablespoon of water to create a slurry. Pour the reserved marinade into the pan and bring to a simmer, gradually stir in the cornstarch slurry, and cook until thickened.

Return the cooked steak to the skillet, tossing gently with the sautéed vegetables and thickened sauce. Cook for another minute to heat everything through.

Serve your Pepper Steak with Bell Peppers and Onion immediately over a bed of steamed rice or noodles.