Preheat oven to 450 F.
Combine pizza sauce and sweet chili sauce. Spread sauce over pizza crust.
Sprinkle with half of the mozzarella cheese and half of the stilton cheese.
Cut apple in half then core and slice into thin wedges. Arrange apple over cheese then top with remaining cheese.
Cook pizza 7-10 minutes until pale golden and starting to bubble. Add prosciutto and cook 2-3 minutes until golden and bubbling.
Serve with fresh arugula and basil. Sprinkle with toasted walnuts, if desired.