Cut the tomatoes in half and scoop out the insides to form a bowl. Chop the tomato pulp and put it into a large bowl. Chop the reserved steak and add it to the bowl along with the reserved couscous and chopped parsley. Mix to combine. Stuff each tomato half with the couscous mixture and put them on a baking sheet. Sprinkle a tablespoon of cheese onto each tomato, then broil until the cheese is melted and bubbling, about 1 to 2 minutes. Transfer the tomatoes to a serving platter and serve hot.