1. Heat oven to 425 degree F. In a medium bowl, combine tomatoes, oil, thyme, salt, and pepper and toss to coat. Turn tomatoes out onto a jelly-roll pan, cut-side up. Roast until tomatoes have softened and given up some of their juices, about 12 minutes. Let cool in pan 5 minutes.
2. Reduce oven temperature to 350 degree F. Arrange phyllo pastry shells on a large cookie sheet. Place a piece of cheese and a tomato half side by side in each pastry shell. Bake until the cheese is melted and bubbly, 5 to 8 minutes. Let cool about 3 minutes before serving. Top each tartlet with a parsley leaf, if desired. Serve hot. Makes 30 tartlets.