Put the breadcrumbs into a mixing bowl, pour over the milk, then leave to soak for 10 minutes until the milk is absorbed. Add the pork mince (ground pork), Parmesan, egg, lemon zest, garlic, ground fennel seeds, parsley and a generous seasoning of salt and pepper.
Mix with your hands until evenly combined then shape into 4 even-sized burgers. Chill in the fridge for 1 hour to firm up, or leave for up to 24 hours if you like.
When you are ready to cook, take the burgers from the fridge and brush on both sides with the olive oil. Fire up the barbecue ready for direct cooking. When hot, put the burgers on the grill bars, lower the lid and cook for 8 minutes on each side.
Pork mince is prone to sticking. Test the burgers are ready by sliding a metal spatula under a corner of one burger. If it comes away easily from the grill and has a deep caramelized crust, it’s ready to turn. If it’s stuck, leave it for a further minute or two before turning, then grill until cooked through.
Once the burgers are on the grill, brush the aubergine (eggplant) slices with a little extra oil, then lay them alongside the burgers to cook, turning them a few times until lightly charred and tender all the way through.
Toast the ciabatta rolls, cut-sides down, for a minute or two on the grill. To serve, put some rocket (arugula) onto the base of the bun and top with a burger. Add a couple slices of aubergine, and top with a dollop of tomato relish or ketchup, if using, before adding the bun lid