Lightly pound the pork chops, at least two times per side.
In a medium bowl, make the marinade by mixing together the orange juice, sugar, soy sauce, black soy sauce and salt. Add the pork chops and coat, let sit for 20 minutes.
Meanwhile make the sauce by mixing 125ml orange juice, white vinegar, tomato ketchup, sugar and cornflour together in a bowl. Set aside.
Heat a large frying pan with 1 tablespoon oil over high heat. Fry the pork chops until both sides turn brown, 3-5 minutes. Turn the heat to medium and continue to cook the pork chops until cooked through, 3-5 minutes.
Add the sauce and mix well. Turn off the heat and add the mandarins. Stir to mix. To garnish, top with orange zest.
Black soy sauce is darker, thicker and sweeter than ordinary soy sauce. You can find it in Chinese/Oriental supermarkets.