Fill a large pot with lightly salted water and bring to a rolling boil over high heat. Once the water is boiling, stir in the noodles and return to a boil. Cook uncovered, stirring occasionally until the pasta has cooked through but is still firm to the bite, about 5 minutes. Drain well in a colander set in the sink.
Whisk together the 3 tablespoons soy sauce, 3/4 cup sweet chilli sauce, 1/2 teaspoon garlic powder, the ground ginger and the sesame oil in a large bowl; add the drained noodles and toss to coat; set aside.
Whisk together the 1/2 cup soy sauce and 1/2 teaspoon garlic powder in a large bowl; add the pork and stir to coat. Allow to marinate 5 minutes.
Heat the cooking oil in a wok or a large, deep frypan over medium-high heat. Add the pork, onions, and chilli flakes to the oil; cook until the pork is browned completely. Stir in 3 tablespoons sweet chilli sauce, the Chinese cabbage, celery, carrots and capsicums; cook and stir until vegetables are completely heated, about 5 minutes. Whisk together the cornflour and water and add to the stir fry, stirring until the mixture thickens. Serve the stir-fry over the noodles.