Place all of the ingredients, except for the oil, mussels, tomatoes and lemon, into a food processor and blend to a rough paste. Loosen the mixture by mixing in a bit of vegetable or sunflower oil.
Heat a wok until smoking, then add the paste. Fry for 1-2 minutes, then add the mussels and cover with a lid. Cook for 3-4 minutes, or until the mussels have opened. Discard any mussels that remain closed. Stir in the chopped tomatoes.
To serve, pile the mussels into a large bowl and serve with lemon wedges.