Add the potatoes, onions, salt, and pepper and cook over medium-low heat for 15 to 20 minutes, turning occasionally with a flat spatula, until the potatoes are evenly browned and cooked through. (Allow the potatoes to cook for 5 minutes before turning.) Turn off the heat and add the parsley, scallions and ham. Reheat on top of the stove or over a hot charcoal grill.