Bring a large pot of salted water to a boil. Add the fusilli and cook according to package directions until al dente, about 8-10 minutes.
While the pasta cooks, prepare the vegetables: halve the cherry tomatoes, dice the cucumber, thinly slice the red onion, and chop the parsley.
In a small bowl, whisk together the olive oil, lemon juice, Dijon mustard, minced garlic, salt, and black pepper to make the dressing.
Drain the cooked pasta and rinse briefly under cold water to cool it slightly. Transfer to a large mixing bowl.
Add the prepared vegetables and parsley to the bowl with the pasta. Pour the dressing over the top.
Toss everything together until well combined. Taste and adjust seasoning with more salt or pepper if needed.
If using, stir in the feta cheese and black olives. Let the salad sit for 5 minutes to allow flavors to meld before serving.
