Season the pork both sides generously with salt and black pepper. Add oil into a pot and heat until very hot over high heat. Sear the meat on both sides on medium-high heat until well-browned. Turn down the heat to medium and add in the sliced onion. Cook until the onion is translucent and has softened.
Add in the juice, water (or stock) and bay leaf. Turn up the heat, cover and bring it to a boil. Reduce the heat to low and simmer gently for 1 1/2 to 2 hours, flipping the meat occasionally. The sauce should have reduced and thickened.
Remove the meat and slice it thinly. Transfer the meat onto a serving plate. If the sauce is not thickened enough, boil and reduce the sauce. Season to taste, if needed, and spoon the sauce over the meat. Serve immediately with rice or other sides.