Prepare Miso Sauce: Mix white miso, sake, mirin, soy sauce, water, kombu (or MSG), and 1/4 tsp cornstarch until smooth.
Prepare Vegetables: Cut cabbage (thick part) and green onion into bite-sized pieces.
Prepare Chicken: Mix chicken breast with 1 pinch salt, 1/2 tsp cornstarch, and 1 tbsp water. Stir until water is absorbed (about 30-40 seconds). This keeps chicken moist.
Make Garlic Paste: Mix garlic and toban djan (chilli bean sauce) to form a paste.
Cook Chicken: Heat 1/2 tsp neutral oil in a pan over medium heat. Add chicken and cook until lightly browned on one side, about 10-15 seconds on the other side. Avoid over-browning to keep chicken moist.
Cook Vegetables: Add 1/2 tsp neutral oil to the pan. Add cabbage and green onion with 1 pinch salt. Hold the pan steady on the flame without shaking to keep heat even.
Add Water and Stir-Fry: Add about 1.5 tbsp water to help cook vegetables and scrape up flavorful bits from the pan bottom. Cook for 20-30 seconds. Avoid adding too much water to prevent watery stir-fry.
Add Miso Sauce and Garlic Paste: Add the prepared miso sauce and garlic paste to the pan. Stir and cook for about 1 minute until sauce lightly boils and aroma develops. Ensure no water leaks to keep umami packed.
Serve: Serve the chicken and vegetable stir-fry over cooked rice.