This sweet and sour vegetable stir-fry is a classic dish that never fails to satisfy. Made with a colorful mix of vegetables like bell peppers, carrots, onions, and pineapple, this stir-fry is both sweet and tangy. The vegetables are stir-fried until crisp-tender and then coated in a delicious sweet and sour sauce. The sauce is made with vinegar, ketchup, soy sauce, and a touch of sugar for the perfect balance of flavors. Serve this sweet and sour vegetable stir-fry over steamed rice for a tasty and fulfilling meal.