Watermelon can be air-fried for a delicious sandwich topper. If you want your fruit crispier, cook it on 80C for several hours, checking every hour or so. We sprinkled thinly sliced watermelon strips in a little sea salt and cracked black pepper and cooked them at 180C for 15 minutes until lightly dried and still soft. You could also use the oven and a parchment-lined tray to cook the melon.