Sauté mushrooms in sesame oil until softened, 2 minutes. Add soy sauce, oyster sauce, carrots and celery, cooking 1 min more. Add wood ear mushroom if using, water and cabbage and cook until slightly wilted. Season with sugar, pepper, and more soy sauce/ oyster sauce as desired (flavor should be mild vegetal/mushroom). Remove from heat and cool. Add green onion and roll small handfuls, about ¼ cup of filling, in eggroll wrappers, using egg wash to seal edges. Fry in vegetable oil, moving constantly, until golden and puffed on all sides, about 4 minutes.