In a large pot, bring salted water to a rolling boil. Add the rotini pasta and cook for 8-10 minutes until al dente. Drain and rinse with cold water.

Chop the English cucumber, grape tomatoes, bell pepper, and red onion into bite-sized pieces. Set aside in a large mixing bowl.

Combine the cooled pasta with the chopped vegetables. Add Italian dressing and sliced black olives if using, then sprinkle fresh parsley. Toss gently to mix.

Carefully fold in crumbled feta cheese, seasoning with salt and black pepper to taste. Adjust as needed.

Cover the bowl with plastic wrap and refrigerate for at least 2 hours to allow flavors to meld.