Set a large pot of water over high heat. Once boiling, add 1 tablespoon salt and fusilli pasta. Stir once, then cook according to package instructions. Drain the pasta and rinse with cold water. Shake off the excess water. Then pour the pasta into a large salad bowl.
Meanwhile, prep the produce. In a small bowl, mix the mayonnaise, Dijon mustard, and anchovies.
Pour the mayonnaise dressing over the pasta and toss well to coat. Then add the tuna, tomatoes, scallions, olives, pepperoncinis, parsley, and capers. Gently toss to mix. Taste, then salt and pepper as needed. Cover and chill until ready to serve.