Place rounds on 2 parchment paper lined 15x10 inch jellyroll pans. Crimp edges, if desired. Spread rounds evenly with dijon mustard; top with cheese slices, tomato, thyme, salt and pepper. Sprinkle rounds with shredded cheese; drizzle with oil. Bake at 425 for 15 minutes or until pastry is golden. Garnish, if desired. Serve immediately. Makes 1 dozen tarts.