1 cup shredded English cucumber
1/4 cup low-fat plain yogurt
3 tablespoons tahini
2 tablespoons lemon juice
1/2 teaspoon salt, divided
1 tablespoon garlic powder
1 teaspoon curry powder
1/2 teaspoon freshly ground pepper
1 pound boneless, skinless chicken breast, trimmed
1 tablespoon canola oil
4 6-inch whole-wheat pita breads or lavash
1 medium tomato, chopped
2 cups thinly sliced romaine lettuce