Boil 150 grams of Hakka noodles as per the instructions on the packet. Drain and set aside to cool.
Heat oil in a deep frying pan and deep-fry the boiled noodles until they turn crispy. Remove from oil and place on a paper towel to drain excess oil.
In a separate pan, heat 2 tablespoons of oil and sauté 1 finely chopped onion, 1 julienned carrot, 1/2 cup shredded cabbage, 1/2 cup thinly sliced bell peppers, and 1/2 cup thinly sliced beans for 3-4 minutes on medium heat.
Add 2 tablespoons of soy sauce, 1 tablespoon of tomato ketchup, 1 tablespoon of red chili sauce, 1 tablespoon of vinegar, and salt to taste. Mix well and cook for another 2 minutes.
In a small bowl, mix 1 tablespoon of cornstarch with 1/4 cup of water. Add this mixture to the vegetables and cook until the sauce thickens.
Place the crispy noodles on a serving plate and pour the vegetable sauce mixture over the noodles. Garnish with chopped spring onions and serve hot.