Arrange a third of the tomato slices in a single layer on a double thickness of heavy-duty foil (about 12 in. square). Place half of the cheese over tomatoes; sprinkle with 1 teaspoon oregano and drizzle with 1 teaspoon oil. Sprinkle with a dash of pepper. Repeat layers.
Top with remaining tomato slices. Drizzle with remaining oil and sprinkle with remaining oregano and a dash of pepper. Fold foil around mixture and seal tightly.
Grill, covered, over medium heat for 8-10 minutes or until heated through. Open foil carefully to allow steam to escape. Transfer to a serving platter; serve with toasted baguette.