To make Tahini Sauce: In bowl, mix tahini, lemon juice and water. Stir in garlic, parsley and salt. Makes 1 cup (250 mL). Set aside.
To make Chicken Falafel: Cut chicken crosswise into thin strips. In nonstick skillet or wok, heat oil over medium-high heat; cook garlic, cumin, coriander, salt, cayenne and chicken, stirring often, until chicken is no longer pink inside, about 5 minutes. Stir in parsley.
Cut off top third of each pita; invert and place in bottom third. Fill each with some of the tahini sauce, the chicken, lettuce, cucumber and tomatoes. Drizzle with remaining sauce.