Preheat the Oven: Preheat your oven to 180 degrees Celsius.
Prepare the Ingredients: Add the quartered onions and sliced apples to a baking tray. Place the pork belly on top. Season the pork belly generously with salt and black pepper, and drizzle with oil.
Apply the Glaze: Mix the gooseberry jam with the apple cider vinegar. Brush the pork belly with this mixture, then place the tray in the oven.
Roast the Pork Belly: Roast the pork belly for 20 minutes. After 20 minutes, brush the pork belly again with the gooseberry glaze. Alternatively, you can also pan-fry the pork belly for a crispy finish.
Crisp the Skin: Increase the oven temperature to 200 degrees Celsius and bake for 10 minutes or until the skin is super crispy.
Serve: Remove from the oven and let it rest for a few minutes. Serve and enjoy!