¼ cup low-sodium soy sauce
2 tablespoons rice wine vinegar
4 teaspoons packed brown sugar
1 tablespoon cornstarch
2 tablespoons vegetable oil, divided
Freshly ground black pepper
1 pound flank steak, thinly sliced against the grain
1 red bell pepper, thinly sliced
1 green bell pepper, thinly sliced
3 cloves garlic, minced
1 tablespoon freshly minced ginger
Cooked white rice, for serving
Make the sauce: In a medium bowl, whisk together the soy sauce, vinegar, sugar, and cornstarch. Set aside.
Heat 1 tablespoon of the oil in a large skillet or wok over high heat. Season the steak with salt and pepper. Add the steak to the skillet and cook, stirring occasionally, until browned on all sides and cooked to desired doneness, about 5 minutes. Remove the steak from the skillet and set aside.
Heat the remaining 1 tablespoon of oil in the skillet over medium heat. Add the bell peppers, garlic, and ginger to the skillet and cook, stirring occasionally, until softened, about 5 minutes.
Return the steak to the skillet and pour over the sauce. Cook, stirring occasionally, until the sauce is thickened and glossy, about 2 minutes.
Serve immediately over rice.