Chicken Salad Pitas

• 1-1.5 lbs (about 8 pieces) cooked, chicken breast tenderloins
• 1/2 cup celery, chopped
• 2-2 1/2 Tbsp. red onion, chopped
• 1/2 cup red seedless grapes, quartered
• 1/4 tsp. garlic powder
• 1/4 tsp. black pepper
• 1/4 tsp. sea salt
• 1/2 cup Greek yogurt, plain