Fill a large pot with lightly salted water and bring to a rolling boil over high heat. Stir in noodles and return to a boil. Cook pasta uncovered, stirring occasionally, until cooked through but still firm to the bite, about 5 minutes. Drain well in a colander set in the sink.

Whisk together 3 tablespoons soy sauce, 3/4 cup sweet chili sauce, 1/2 teaspoon garlic powder, ground ginger, and sesame oil in a large bowl; add drained noodles and toss to coat; set aside.

Whisk together 1/2 cup soy sauce and 1/2 teaspoon garlic powder in a large bowl; add pork and stir to coat. Allow to marinate 5 minutes.

Heat cooking oil in a wok or a large, deep skillet over medium-high heat. Add pork, onions, and red pepper flakes; cook until pork is browned completely. Stir in 3 tablespoons sweet chili sauce, napa cabbage, celery, carrots, and bell peppers; cook and stir until vegetables are heated through, about 5 minutes.

Whisk together cornstarch and water in a bowl; add to stir-fry, stirring until mixture thickens. Serve stir-fry over noodles.