Rinse and pat dry the pork belly. Liberally season the pork with sea salt, pepper and spices. Wrap in plastic wrap and refrigerate overnight to allow pork belly to absorb flavors.
Preheat oven to 275 degrees F.
In a Dutch oven or large cast-iron skillet (the pan should fit the ingredients comfortably without crowding them), add pork belly, apple cider vinegar, bay leaves, shallots and peppercorns. Add enough water to go halfway up the sides of the pork belly. Put in oven, then place a sheet of parchment paper over the pan to cover. Bake for 5 hours.
Remove from oven. Take pork belly out of pan and set aside. Add squash to the pan and return to oven. Cover with parchment paper and cook for 30 to 40 minutes or until soft. When ready to serve, if squash is cool, place in hot oven to reheat.
Heat a medium skillet (cast iron is preferred) over medium-high heat. Sear the top and bottom until browned and crispy (about 45 seconds each side). Remove from pan. Slice pork belly into 1-inch-wide pieces. Serve with squash.