In a large non-stick skillet over medium heat, brown the pork slices in the oil. Drain the oil and reposition the pork in the skillet. Add the onions overtop, cover and cook for 2 minutes. Add the maple syrup and soy sauce. Cover again and simmer for 10 minutes. Uncover and let the sauce reduce until almost dry, stirring halfway through cooking. Season with pepper and set the pork aside on a plate.