Heat oven to 400 degrees. In the bowl of a food processor, combine the parsley, garlic, red-pepper flakes, and breadcrumbs. Pulse until breadcrumb mixture is combined.
Remove all of the seeds and juice from the tomatoes. Using a spoon, fill the remaining tomato flesh with the breadcrumb mixture. Place the stuffed tomatoes in a shallow baking dish.
Drizzle tomatoes with oil; season with salt and pepper. Add 1/2 cup water to bottom of baking dish. Cover dish tightly with foil.
Bake tomatoes until they are tender and the stuffing has cooked through, about 45 minutes.
Heat broiler. Remove baking dish from oven; remove aluminum foil. Broil until crisp and slightly browned, 2 to 3 minutes. Serve.