Preheat oven to 450 degrees F. Arrange tomato halves, cut sides up, in a foil-lined 15x10x1-inch baking pan. Sprinkle with oregano and salt; drizzle with the 1/4 cup olive oil. Roast tomatoes, uncovered, for 45 minutes or until browned and shriveled. Remove and cool. Coarsely chop the tomatoes. Place in a medium bowl and stir in parsley; set aside.
Preheat broiler. Cut each slice of pancetta into thirds. Arrange pancetta on the rack of an unheated broiler pan. Broil 3 to 4 inches from the heat for 2 to 3 minutes or just until golden and crisp, turning once. Set aside.
Cut the loaf of bread in half lengthwise. Drizzle the cut sides of each half with the 2 tablespoons olive oil. Cut each half of the bread crosswise into 8 slices. Top slices with tomato mixture and pancetta. Makes 16 pieces.