Brush the mussels thoroughly with a hard brush under running water and rinse. Chop the brown onion, ginger, chiles, shallots, and crush the garlic. Heat the oil in a frying pan and roast the chopped vegetables for three minutes. Add the tomato sauce, sugar, and fish stock. Bring to a boil and season with salt and freshly ground black pepper. Add the mussels, reduce the temperature and simmer for about 3-4 min. until all the mussels have opened. Later, place the mussels on a serving platter.
Mix the corn flour with a tiny bit of cold water, pour it into the sauce and let it thicken leisurely, then pour it over the mussels.