Cut cabbage, carrot, and onion into bite-sized pieces.
Add cooking oil to a pan and stir-fry the vegetables.
Once the vegetables are softened, add soy sauce, sugar, mirin, and water to make the sauce.
When the sauce starts to boil, add pepper and minced garlic, then simmer over high heat for a short while.
Place the stir-fried vegetable sauce over rice.