Preheat oven to 400°.
Cut tops off tomatoes; discard. Carefully seed tomatoes, leaving shells intact. Sprinkle the cut sides of tomatoes with 1/4 teaspoon salt. Place tomatoes, cut sides down, on several layers of paper towels; drain for 15 minutes.
Place bread in a food processor; pulse 10 times or until coarse crumbs form to measure 1/2 cup. Combine breadcrumbs, 6 tablespoons parsley, cheese, and garlic in a small bowl.
Heat the oil in a large nonstick skillet over medium-high heat. Place the tomatoes, cut sides down, in pan, and saute for 5 minutes. Remove pan from heat; turn the tomatoes over. Spoon about 2 tablespoons breadcrumb mixture over each tomato. Spray the breadcrumb mixture with cooking spray, and sprinkle with 1/4 teaspoon salt and pepper. Wrap the handle of the pan with foil. Bake at 400° for 30 minutes or until the breadcrumb mixture browns. Garnish with thyme leaves, if desired.