In a mortar and pestle pulverize (or puree in blender) the garlic, anchovy fillets, and the pulp of the tomatoes. Add a small pinch of salt and pepper, to taste, and thin with the lemon juice. Set this aside.
In a deep-sided frying pan, saute the onion in olive oil and cook until translucent. Add the mussels and white wine and bring to a boil. Cover and simmer until the mussels open, approximately 10 minutes.
Remove the mussels from the pan and arrange in a serving bowl. Leaving the juice in pan, add the pulverized anchovy, garlic, and tomatoes to pan juices. Pour the juice over the mussels and decorate with lemon wedges. Serve with toast tips.