Drain the anchovies and place in a heavy bowl with garlic and tomato paste. Mash the mixture to a smooth puree. Dribble in the oil, a few drops at a time, stirring until the mixture becomes thick and smooth. Stir in the lemon juice (or vinegar) and pepper. Preheat the oven to 500 degrees F. Brown the bread lightly on one side. While the bread is still warm, spread the untoasted side with the anchovy mixture. Arrange the bread on a baking sheet and bake for 10 minutes. Sprinkle with parsley and serve at once.