In a small container, mix together the soy sauce, oyster sauce, sugar, ketchup, and rice vinegar.
Bring a pot of water to a boil. Once it starts to boil, add in the noodles. Cook for only 3 minutes for fresh noodles (or according to the package instructions for other types of noodles).
Drain the noodles and set aside. You can add about 1 teaspoon of sesame oil to keep the noodles from sticking together, if you're not quite ready to continue making the dish.
In a large wok or pan, heat 1 tablespoon oil over medium-high heat. Add the chopped garlic and ginger. Saute for 30 seconds or until fragrant. Add the onion, cabbage, carrot, and mushrooms. Stir-fry for 2 to 3 minutes.
When the vegetables are cooked but still crunchy, add the drained noodles and sauce. Toss everything together for 2 to 3 minutes or until the noodles are nicely coated.
Garnish with green onions and serve with the pork belly.