Lightly spray or brush the naan/flatbreads with water. Place flatbreads on the grill/grillpan and grill for about 1-2 minutes, so that you have grill marks on one side.
Transfer the flatbreads grilled side up on a cutting board.
Spread the onion jam over the flatbreads and arrange the Castello cheese on top, followed by the grapes, prosciutto and red onion. Season very lightly with salt and pepper, and sprinkle with a thyme.
Return the flatbreads on the grill/grillpan, cover and let it cook for about 7-10 minutes, or until the grapes are just about ready to burst, the cheese has softened, and the flatbread is toasted. Remove from grill, slice, and enjoy immediately.