Combine pork belly and pork loin in a large bowl. Toss with 1 tablespoon groundnut oil to coat. Add garlic, ginger, red chile, peppercorns, brown sugar, bay leaves, and cumin. Mix in diced apple, cider vinegar, and soy sauce. Stir to coat the pork. Marinate in the fridge, stirring occasionally, for at least 1 hour.
Heat remaining 1 tablespoon oil in a deep pan over medium heat. Melt 1 tablespoon butter in the pan and sprinkle in salt and pepper. Add onion, bell pepper, and mushrooms. Fry until softened, about 5 minutes. Add the pork and marinade; cook until pork starts to brown, about 6 minutes. Stir in lemonade, cornstarch, and bouillon; sauce should cover the pork and vegetables.
Reduce heat and simmer, covered, until liquid is reduced and pork is tender but still slightly pink in the center, about 1 hour. An instant-read thermometer inserted into the center should read at least 145 degrees F (63 degrees C). Add the remaining 1 tablespoon butter 10 minutes before pork is finished cooking. Discard bay leaves before serving.
