Preheat oven to 190 degrees celsius (slightly lower if using fan-forced).
Trim the sides of the puff pastry sheets so that they resemble long rectangles.
Use a knife to carefully score a line approximately 2cm from each of the outside edges (but don't cut all the way through).
Prick the pastry sheets with a fork and place into a preheated oven for 15 minutes.
Thinly slice the pears.
Remove the puff pastry sheets from the oven and allow to cool slightly.
Spread the caramelised onion over the middle of each pastry sheet (up to the scored lines).
Place the pear slices onto the caramelised onion (allowing them to overlap slightly).
Cook in the oven for a further 5-10 minutes or until the pear is just starting to soften.
Remove from the oven and crumble over the goats cheese.
Season with salt and pepper (optional).
Sprinkle over small pieces of prosciutto (simply tear the slices by hand).
Finely grate the parmesan cheese over the top and sprinkle over the walnuts.
Serve with lemon wedges.