Preheat oven to 375°F. Lightly coat a 9-by-13-inch baking dish with cooking spray.
Combine 5 cups tomatoes, 1½ cups rice, minced garlic, 1 tablespoon oregano and ½ teaspoon each ground pepper, crushed red pepper (if using) and salt in the prepared dish. Carefully pour in 3 cups boiling water; stir until the mixture is well combined and the rice is fully submerged. Nestle 1 (6-ounce) block feta in the center of the mixture. Tightly cover the dish with foil. Bake, undisturbed, until the rice is tender and the tomatoes are soft, about 1 hour. Remove the foil and continue baking until the liquid has evaporated, about 15 minutes more.
Increase oven temperature to broil. Broil until the feta is lightly browned, 2 to 3 minutes. Remove from oven and stir until the feta is broken into small pieces throughout the rice mixture. Garnish with oregano, if desired.
