1. Wash the mussels and DISCARD any that stay open.
2. In a large frying pan, sauté the garlic, oregano and tomatoes in the butter for one minute.
3. Add the pepper, salt, wine, fish stock and mussels.
4. Cover and let steam for 5 minutes or until the mussels are open.
5. Sprinkle with the chopped basil.
6. Serve with lemon slices.