For the watermelon and mozzarella stack, cut the watermelon slices into 4cm/1.5in x 7.5cm/3in pieces. You want 12 pieces in total.
Lay four slices of pancetta horizontally onto a board, so they overlap slightly, and place a piece of watermelon in the centre, across the slices of pancetta. Season, to taste, with salt and freshly ground black pepper.
Top the piece of watermelon with a slice of mozzarella and season with a little more salt and freshly ground black pepper.
Fold the sides of the pancetta over the mozzarella to create a parcel, leaving each end of the watermelon exposed.
Repeat the above until you have 12 parcels in total.
Heat a frying pan until hot then add the parcels, three or four at a time, depending on the size of your pan. Fry on each side until the pancetta is crisp and golden-brown - take care not to overcook because you don't want to melt the mozzarella.
Remove the parcels from the pan, drain on kitchen paper and keep warm. Repeat with the remaining parcels.
For the salad, place the watermelon into a mini food processor and blend to a smooth purée. Transfer to a bowl and whisk in the sherry vinegar and olive oil. Season, to taste, with salt and freshly ground black pepper.
Just before you're ready to serve, toss all the salad leaves together and dress with a little of the watermelon dressing.
To serve, stack three warm watermelon parcels onto each of four serving plates. Place the salad to one side and drizzle over a little extra watermelon dressing.