1. Heat oil in saucepan over medium heat. Add onion and celery, and cook 5 minutes, or until soft. Add cumin and garlic, and sauté 1 minute. Stir in spinach and drained tomatoes. Cook 5 minutes, or until most of liquid has evaporated.
2. Stir in black beans, quinoa, carrots, and 2 cups water. Cover, and bring to a boil. Reduce heat to medium-low, and simmer 20 minutes, or until quinoa is tender. Stir in 1 cup cheese. Season with salt and pepper, if desired.
3. Preheat oven to 350°F. Pour liquid from tomatoes in bottom of baking dish.
4. Fill each bell pepper half with heaping ¾-cup quinoa mixture, and place in baking dish. Cover with foil, and bake 1 hour. Uncover, and sprinkle each pepper with 1 Tbs. remaining cheese. Bake 15 minutes more, or until tops of stuffed peppers are browned. Let stand 5 minutes. Transfer stuffed peppers to serving plates, and drizzle each with pan juices before serving.