Boil a large stock pot of water; add chicken breasts. Bring back to boil then reduce to a simmer.  Cook until the chicken is no longer pink inside, approximately 30 minutes.

Remove fully cooked chicken and allow to cool to the touch; shred into smaller pieces and place in a large mixing bowl.

Chop onion, halve grapes and olives; add to mixing bowl with chicken.

In a separate, smaller bowl, add the mayo, yogurt, juice of half the lemon, chopped, fresh parsley, salt and pepper.  Mix well.

Add mayo mixture to chicken and blend well, coating evenly.

Slice pitas in half, add some spinach and then stuff with chicken salad.  Serve with pepper slices on the side.