Peel and finely chop the onion and clove of garlic. Heat the butter, fry the onion and garlic in it until translucent. Add the vegetables, fry them and season with herb salt and pepper. Wash and slice the tomatoes. Put the Pak Choy in a greased casserole dish, spread the tomatoes on top and sprinkle everything with the parmesan. Bake the dish in a hot oven at 200 ° C for about 5 minutes.