Clean the mussels thouroughly. You clean them by rubbing the shell very well under running water. If there are any barnacles or stuck stones, residue of other broken shells you might need to scrape them off with a small knife or rub it thoroughly to remove everything. 

Discard all mussels that are already open. 

Then, using a small knife, remove their beard. 

Place the healthy, closed mussels for only 2-3 minutes in a little boiling water or even better in a little wine, until they open, a sure sign that they are still alive. Throw away the ones that don't open. 

Heat the oil in a frying pan and sauté the onions cut into round slices. 

When the onions are tender add the cloves of garlic and continue sautéing for 2-3 minutes to let out their flavor. 

Add the washed mussels, cover the frying pan and cook over strong heat for a few (2-3) minutes, stirring a couple of times with a wooden spoon. 

Add the freshly ground pepper, a generous amount of the parsley (but not all of it), the lemon juice (keep a little to sprinkle over the ready mussels later), one dose of oregano and finally, the wine. Cook for an additional 4 minutes, stirring well in the meantime so that everything combines for a nice flavor. 

Leave them in the frying pan for a while so that a bit more of the wine evaporates in the meanwhile and serve hot, as they are in their shells, sprinkled with the rest of the parsley and some of the leftover stock. 

Sprinkle each plate with a little uncooked lemon juice, just before you start sucking them. Because mussels cooked this way are sucked from their shells, not eaten with a fork.