1/4 c. low-sodium soy sauce
2 tbsp. rice wine vinegar
4 tsp. packed brown sugar
1 tbsp. cornstarch
2 tbsp. vegetable oil, divided
Freshly ground black pepper
1 lb. flank steak, thinly sliced against the grain
1 red bell pepper, thinly sliced
1 green bell pepper, thinly sliced
3 cloves garlic, minced
1 tbsp. freshly minced ginger
Cooked white rice, for serving
Make sauce: In a medium bowl, whisk the soy sauce with the vinegar, sugar, and cornstarch. Set aside.
In a large skillet over high heat, heat 1 tablespoon oil. Add flank steak, season with salt, and cook until cooked through and seared on all sides, about 8 minutes. Remove steak to a plate.
Add 1 tablespoon remaining oil and red and green bell peppers to the skillet. Cook until softened, about 4 minutes. Add the garlic and ginger and cook stirring until fragrant. Return the beef to the skillet and pour over prepared sauce. Cook, stirring, until the sauce is glossy about 2 minutes more.
Serve with rice.