Heat a grill pan over medium-high heat. Coat pan with cooking spray. Combine cumin, paprika, salt, and turmeric in a small bowl. Rub spice mixture evenly over turkey. Add turkey to pan; cook 3 minutes on each side or until done. Remove turkey from pan.
Cut off top third of each pita; reserve for another use. Add pitas to pan; grill 30 seconds on each side or until marked. Cut turkey into slices. Divide turkey, cucumber, and bell pepper evenly among pitas.
Combine tahini and remaining ingredients in a small bowl, stirring with a whisk. Serve tahini mixture with sandwiches.
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