Begin by making the cashew cream. If using mozzarella you can skip this step. Place the drained cashews, 1/4 cup water, lemon juice and salt in a blender. Blend until smooth and creamy. Place into a small serving jar and refrigerate.
Place a small grill pan over a medium-low heat. Bring to the pan to temperature and lightly brush with the oil. Slice the nectarines. You can go with big chunky slices or slivers as I have. The choice is yours. Place half the nectarine slices in the pan and leave for a minute before flipping over. Cook for another minute before removing to a plate and repeating with the remaining nectarine.
Toss the rocket (arugula), basil and watercress together in a serving bowl. Top with the grilled nectarines and drizzle the balsamic syrup over the top. Add a few dollops of the cashew cream (or mozzarella, if using) and finally the chopped hazelnuts. Serve immediately.