How to Make It
Combine tahini, 2 tablespoons water, 2 teaspoons juice, 1 1/2 teaspoons oil, 1/8 teaspoon salt, and garlic in a small bowl, stirring with a whisk.
Sprinkle chicken with remaining 1/4 teaspoon salt and pepper. Heat a grill pan over medium-high heat. Coat pan with cooking spray. Add chicken to pan; cook 5 minutes on each side or until done. Remove chicken from pan; let stand 5 minutes. Add pitas to pan; cook 1 minute on each side or until lightly toasted. Slice chicken thinly across the grain.
Combine remaining 1 1/2 teaspoons oil and remaining 2 teaspoons juice in a medium bowl, stirring with a whisk. Add lettuce; toss to coat. Divide lettuce mixture, chicken, and bell peppers evenly among pita halves; drizzle each stuffed pita half with about 1 1/2 teaspoons tahini mixture.