1. Boil the potatoes for about 10 minutes, until they're just tender. Stir fry the onion, carrot, mushrooms, and zucchini.
2. Add in the potatoes and stir for about 30 seconds. Take them off the heat. In a small bowl, completely mix the black bean sauce with water.
3. Pour over the veggies, add the frozen peas, and bring to a boil. Turn the heat down to medium-low and simmer uncovered for 7-10 minutes, stirring occasionally.
4. Spoon some of the sauce into a cup and mix with the cornstarch. Pour this mixture back into the wok and stir well to thicken the sauce.
Serve over hot cooked yakisoba noodles or noodles of your choice.