Pre-heat the oven to 200°C/390°F. Halve ciabatta and spread pesto on top.
Slice tomatoes and onion, lay over the ciabatta, then season with salt and pepper.
Slice mushrooms and lay on top.
Repeat with the mozzarella.
Put in oven and bake for approx. 15 – 20 min. at 200°C/390°F until mozzarella has melted.
Tear prosciutto into small pieces and lay out on hot ciabatta.
Add a good portion of arugula. Tip: drizzle some of your favorite salad sauce or balsamic reduction over it.