Melt the butter in a heavy small skillet over medium heat. Add the anchovies and stir until they dissolve, about 3 minutes. Stir in the herbs, garlic, lemon zest, and crushed red pepper.
Arrange the bread slices on a large baking sheet. Brush with the anchovy mixture. Sprinkle with the cheese. Bake until the cheese melts and the bread is golden, about 10 minutes. Cut the bread slices in halves and serve.