Cube the tuna. Heat oil in skillet over medium. Add tuna and cook until lightly browned on all sides. Transfer to a plate and sprinkle with salt and pepper. Add bell pepper to skillet and cook until it begins to brown about 10 minutes. Add tomato, garlic, rosemary, salt and pepper. Bring to a simmer. Add beans, cover, and reduce to low. Cook for 10 minutes. Stir in tuna and cook for 2 minutes and serve.