MAKES FOUR SERVINGS
Add the tuna, with its oil, to a large bowl, and break it up with a spoon. Finely chop the cucumber, radishes, onion, and celery, and add it to the tuna. Add the sliced olives to the tuna and vegetables. Season the mixture with lemon juice, olive oil, basil, red pepper flakes, and salt. Set the mixture aside, allowing the flavors to meld.
Meanwhile, bring a pot of water to a boil, and salt the water generously - your pasta water should be as salty as the ocean. Boil the Sfoglini Fusilli to al dente, 5 to 8 minutes. When the pasta is cooked, drain and rinse it in cold water.
Add the pasta to the tuna-vegetable mixture, and gently toss to combine. Refrigerate overnight (8-10 hours) to allow the ingredients to blend. Salt the pasta salad to taste, and serve.