Preheat the oven to 300 degrees F (150 degrees C).
Line the Sourdough Bread (8 slice) on two baking sheets.
Divide the Mozzarella Cheese (1 1/2 cup) evenly on each bread slice. Continue the same process with the Gorgonzola Cheese (1 1/2 cup) and Walnut (1 cup).
Place baking sheets in the oven and bake them for 10-12 minutes, or until the cheese is melted.
Place the Arugula (2 cup) in a salad bowl. Add the Garlic (2 clove) and Truffle Oil (2 tablespoon). Toss to combine.
Top each bruschetta with a handful of arugula.
Serve when it is still warm.