· Preheat oven to 350 degrees F (175 degrees C).
· Put peppers into a large pot with just enough salted water to cover; bring to a boil and cook until the peppers are just tender, about 5 minutes. Drain peppers thoroughly.
· Arrange peppers into a shallow baking dish with cavity-side up.
· Mix rice, tuna, celery, onion, and black pepper together in a bowl; add mayonnaise and stir to coat. Spoon the rice mixture into the bell peppers. Pour water into the baking dish around the stuffed peppers.
Bake for 20-25 minutes. Serve and enjoy!