Add celery, olives, cucumber, green onions, and tomatoes to pasta in large bowl.
In a small bowl, whisk together dressing, mayo, oregano and pepper.
Fold dressing and cheeses into pasta- vegetable mixture.
Add tomatoes, folding in gently.
Sprinkle reserved feta on top of salad before serving.
Tips: -I used about 2/3 of the dressing. I think next time I'll cut the mayo to 1/2 cup and try 1 1/4 cup Italian dressing. -Best to make and let sit for a couple of hours in refridge. -I used about 1 1/2 lbs pasta total. -the large can of olives have "6 oz drained weight" label on front of can.