Cut the carefully cleaned pork lung roast (without fat and sinews) into strips and turn them all around in cornstarch. Cut the spring onions into fine rings, the fresh chili peppers into very fine strips and finely chop the garlic. Blanch the tomatoes briefly in boiling water, peel and cut into small cubes. Collect the juice as it comes out. Heat peanut or vegetable oil in a wok or heavy skillet until hot. Sauté onion rings, garlic and chilies briefly until light. Knock off excess cornstarch from meat strips and stir in meat. Fry just briefly until crispy (lung roast about 3 minutes, cheaper meat a little longer depending on quality). In a cup, mix the soy sauce with tomato cubes including juice, salt as well as sugar, pour over the meat and let it boil up briefly. As soon as the sauce starts to become creamy, remove the pot from the heat, sprinkle chopped coriander greens on top and serve.