Greek Salad Pita Pockets with Grilled Chicken

Name: Greek Salad Pita Pockets with Grilled Chicken
Ingredients: 1 lb. chicken breast cutlets; Juice of 1/2 lemon (2 tbsp.); 6 tbsp. extra-virgin olive oil, divided; 1 tsp. dried oregano; 3 small garlic cloves, minced, divided; kosher salt; Black pepper; 1 cucumber, seeded, quartered, and thinly sliced; 1/2 pt. yellow grape tomatoes, halved lengthwise (3/4 cup); 1/2 pt. red grape tomatoes, halved lengthwise (3/4 cup); 1/2 red onion, thinly sliced into half moons (3/4 cup); 1/2 c. crumbled feta; 1/4 c. chopped fresh mint (or parsley_; 1/4 c. pitted Kalamata olives, halved (optional); 2 tbsp. red wine vinegar; 4 whole-wheat pitas, halved and lightly toasted