For the oatmeal omelet with mushroom filling, mix oatmeal with the oat milk and let it swell for about 30 minutes. Chop shiitake mushrooms, onions and garlic.
Wash and cut Chinese cabbage into noodles. For the filling, heat sesame oil in a pan and sauté mushrooms until they begin to brown. Add onion and garlic and sauté briefly.
Reduce heat and saute with lid on for about 10 minutes. Add Chinese cabbage and let it get hot. Season with lemon salt and pepper.
Mix egg and salt thoroughly with soaked oatmeal. Heat sesame oil in a frying pan, pour in the mixture and spread. Fry, not too hot, until the top is bubbled and the bottom is golden brown.
Slide the omelet onto a plate, fill with the mushrooms, fold and serve the oatmeal omelet with mushroom filling while still hot.