Place the apple and fennel slices in a bowl and sprinkle with salt and pepper. Mix the honey, Dijon wholegrain mustards, lemon juice, and olive oil in a jug until well combined. Pour the dressing over the fennel and apple, add the dill, and toss to combine. Set aside until ready to serve.
Heat a non-stick pan over medium-low to medium heat. Place 2 slices of bread in the pan. Add pulled pork, mature cheddar, and caramelised onions to each slice. Add a layer of mozzarella, close the sarmies with another slice of bread, and toast slowly on one side. Flip the sandwich and continue to cook for another 3 to 5 minutes or until golden brown and crispy outside; the cheese should be melted. Remove from the pan, open the top slices of each sandwich and add a bit of apple and fennel salad. Close each sandwich with the top slices and serve immediately with extra salad.