Boil pot of water and cook dry noodles. When thoroughly cooked, drain, rinse with cold water, and set aside.
Heat up a skillet with vegetable oil. Stir-fry onions for 1 minute or until translucent.
Add sliced shiitake mushrooms and stir-fry for 1 minute. Then add the zucchini and cabbage until both cook down, about 3-4 minutes. Lastly, add the scallions and stir-fry for another 30 seconds. Set aside in a separate plate.
In the same skillet at medium heat, add Korean black bean paste and sugar until the sugar has dissolved. Then, add 1 cup of water or vegetable broth. Lower heat to simmer.
Make cornstarch slurry with 1 part cornstarch 2 parts water. Add to black bean sauce mixture.
Add vegetables to black bean sauce and stir until vegetables are evenly coated.
Place noodles in a bowl and top with black bean sauce.
Julienne cucumbers and slice pickled radish to serve on the side.