Best ever pepper steak

INGREDIENTS 1/4 c. low-sodium soy sauce2 tbsp. rice wine vinegar4 tsp. packed brown sugar1 tbsp. cornstarch2 tbsp. vegetable oil, dividedKosher saltFreshly ground black pepper1 lb. flank steak, thinly sliced against the grain1 red bell pepper, thinly sliced1 green bell pepper, thinly sliced3 cloves garlic, minced1 tbsp. freshly minced gingerCooked white rice, for serving DIRECTIONS