Preheat grill to medium-high heat.
Season chicken breasts with salt, pepper, and olive oil.
Grill chicken for 6-7 minutes on each side, or until cooked through.
Remove chicken from grill and let rest for a few minutes. Slice into strips.
In a medium bowl, combine tomatoes, cucumber, red onion, kalamata olives, feta cheese, lemon juice, olive oil, parsley, salt, and pepper. Stir to combine.
Warm pitas on the grill for 1-2 minutes on each side.
Fill each pita with grilled chicken strips and top with Greek salsa.
Serve immediately and enjoy!