In a large bowl, add cooked rotini pasta, tuna, cucumbers, red peppers, celery, and red onions; toss to blend.
Add Roma tomatoes, feta cheese and black olives; gently toss again.
Pour in a little bit of Greek salad dressing and toss before adding a little bit more if needed or until the ingredients are lightly coated; season with salt and pepper.
Before serving, garnish with freshly chopped parsley and toss one more time to mix.