1. Preheat grill or grill pan.
2. Lightly spray or brush the naan with water.
3. Place on the grill for about 1-2 minutes, so there are grill marks on one side. Transfer the flatbreads grilled side up on a cutting board.
4. Spread the onion jam over the flatbreads and arrange the Castello cheese on top, followed by the grapes, prosciutto and red onion.
5. Season very lightly with salt and pepper, and sprinkle with thyme.
6. Return the flatbreads to the grill, cover and let 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.
7. Remove from grill, slice and enjoy immediately.