Walnut basil pesto: add basil, walnuts, garlic cloves and salt to a food processor or blender. Pulse to combine.
When things are chopped well, start slowly adding your olive oil while the processor/blender is running on low. This starts to form an emulsion and gives you the consistency you would want.
When the pesto is smooth and has a thickened consistency, remove from processor/blender to a bowl add parmesan cheese, and stir.
Taste the fully combined pesto and add any additional salt and pepper that you think it might need. Store in the fridge for a few days.
Calabrian chili mayonnaise: in a medium bowl add mayonnaise and crushed Calabrian chilis and whisk to combine. Taste and add a pinch of ground black pepper if desired.
Store in a sealed container in the refrigerator for up to 2 weeks.
Sandwich assembly: slice your Ciabatta rolls.
Add a generous portion of Calabrian chili mayonnaise to the bottom of the roll. Top that with a few slices of prosciutto.
Top the meat with slices of fresh mozzarella and top the cheese with a handful of arugula.
Spread pesto on the top part of the roll and close the sandwich.
Serve and enjoy.