1. Heat the olive oil in a large frying pan over high heat.
2. Add the garlic to the oil and fry for 30 sec.
3. Add the mussels to the hot pan and toss them every 30 sec. or so, until most of the mussels are opened.
4. Squeeze the lemon wedge and drop it in the pan, followed by the white wine and fennel.
5. Cook for 1 minute and add the tomato sauce.
6. Cover the pan with a lid to trap the heat.
7. Cook the mussels for 2-3 minutes more, after they open completely.
8. Season to taste with salt and pepper, and remove any unopened mussels.
9. Before serving the Mussels Marinara, do not forget to remove the used lemon wedge.
Cleaning instructions: Before cooking the mussels, wash them thoroughly in cold water, scrub the shells lightly and pull out the "beards" - the hairy growth that the mussels use to attach themselves to rocks.
Also, check my instructions on How to cook mussels.