In a blender combine juice, 1 tablespoon oil, garlic, coriander, cumin, salt and pepper and mint or cilantro leaves. Process until smooth and pour over chicken to marinate. Refrigerate chicken and allow to marinate for 30 minutes. In a small bowl stir together yogurt, cucumber and chopped mint.
In a large skillet heat 1 tablespoon olive oil over medium high heat. Add marinated chicken and cook for 8-10 minutes, stirring occasionally. Heat pitas under a broiler or in a toaster oven. Slice open pitas and stuff with chicken, tomatoes, lettuce and top with yogurt dressing. Serve immediately.