In a food processor or blender, blend the baby arugula, lemon juice and olive oil until smooth. Set aside.
Remove the rind from the watermelon slices. Cut the slices into circles by trimming off the corners of the watermelon slices.
Place a slice of watermelon on a plate; spread a thin layer of pesto onto the slice, followed by a slice of Galbani® Fresh Mozzarella. Repeat layers offset on the previous layer.
Garnish with chopped green onion.