Pre-heat the oven to 190° C. Heat the groundnut oil in a large casserole dish over a moderate heat until hot. Season the pork then seal for a few minutes all over. Remove from the heat and stir through the red onion and sliced apple. Spoon into a cast iron deep skillet. Prepare the topping by pulsing the flour and butter in a food processor until it resembles rough breadcrumbs. Spoon into a mixing bowl and stir through the cheese and some seasoning. Sprinkle on top of the pork filling. Bake for 30-40 minutes until the crumble topping is golden and cooked. Remove from the oven and leave to rest for 5 minutes before serving. For top tips on protecting you and your family when preparing raw meat and poultry, visit Food Safety in the Home.