Preheat oven to 350 degrees F (175 degrees C). Prepare a 2-quart casserole dish with cooking spray.
Spread long-grain rice into prepared casserole dish.
Heat olive oil in a saucepan over medium heat. Cook and stir carrot, celery, and onion in hot oil until onion is soft and translucent, about 4 minutes. Stir garlic into mixture; cook and stir 1 minute more. Increase heat to high; add chicken stock and bay leaf to the saucepan and bring to a boil. Pour the mixture over the rice in the casserole dish. Cover the dish tightly with aluminum foil.
Bake in preheated oven 20 minutes. Remove aluminum foil and continue baking until the rice is tender and has absorbed most of the liquid, about 20 minutes more. Remove and discard bay leaf; season with black pepper. Fluff with a fork to serve.