Clean the mussels thoroughly under running water with a root brush, also removing the beards hanging on the outside. Discard any mussels that do not close during this process.
Peel and chop garlic and shallots. Rinse parsley and chop not too small. Blanch (scald) tomatoes, skin, seed and dice the flesh.
Heat the butter in the sauté pan and sauté the shallots, garlic and thyme. Pour in the mussels and place the lid on top. Stir or shake several times until all the mussels have risen. Add the lemon peel, a little bit of parsley and pepper to the risen mussels. Using a slotted spoon, place the mussels in a preheated tureen, discarding any mussels that have not been opened.
In the remaining juice in the sauté pan, heat the diced tomatoes and add the pastis and cook briefly. Pour this sauce over the warm mussels, sprinkle with the remaining parsley and serve immediately.
Serve with a piece of good baguette.