Bring a large pot of salted water to a boil. This helps to flavor the pasta as it cooks.

Add the fusilli pasta and cook according to package instructions until al dente, usually about 8-10 minutes.

Once cooked, drain the pasta in a colander and rinse under cold water to stop the cooking process and cool it down.

In a large mixing bowl, combine the drained tuna, halved cherry tomatoes, diced cucumber, finely chopped red onion, sliced black olives, and chopped parsley.

Gently mix the ingredients together with a spatula, being careful not to break up the tuna too much.

In a small bowl, whisk together the olive oil, lemon juice, Dijon mustard, minced garlic, salt, and black pepper until well combined. This emulsifies the dressing, ensuring a smooth texture.

Add the cooled pasta to the tuna mixture in the large bowl.

Pour the dressing over the pasta and tuna mixture, and gently toss everything together until evenly coated.

Taste and adjust seasoning if necessary, adding more salt or pepper as desired.

Cover the salad with plastic wrap and refrigerate for at least 30 minutes to allow the flavors to meld.

Serve chilled, garnished with additional parsley if desired.