The fiery and bold flavors of Szechuan cuisine are brought to life through the sauce. Create a mouth-watering sauce by combining soy sauce, vinegar, hoisin sauce, chili paste, and a hint of sugar for balance. This combination adds layers of umami, tanginess, and spiciness to the dish. Toss the cooked beef and vegetables in the sauce, ensuring they are evenly coated, and allow them to simmer briefly to meld the flavors together.