To make the tzatziki sauce, add the yogurt, cucumber, garlic, dill, lemon juice, 1/2 tsp salt and 1/8 tsp black pepper in a food processor and process until smooth. Transfer to a bowl and place in the refrigerator until ready to use.
Season chicken breasts with mediterranean seasoning, salt and black pepper, to taste. Cook in a large skillet or pan over medium heat 5-6 minutes on each side until cooked through. Cut into strips.
Top pita with lettuce, chicken, peppers, onions and tzatziki sauce. Fold pita over and serve.