Boil the rotini according to the package instructions to al dente, about 8-10 minutes, adding a pinch of salt to the water. Once cooked, drain and rinse under cold water to cool the pasta.
In a large bowl, combine the cooled pasta, cucumber, tomatoes, feta cheese, black olives, and red onion. Drizzle with the Italian dressing and toss until everything is well coated.
For the best flavor, let the salad chill in the refrigerator for at least 1 hour before serving. This allows the flavors to meld together beautifully.