To prepare the turkey, in a shallow flat dish, combine paprika, onion salt, garlic powder, cayenne pepper, fennel, thyme and white pepper. Rub mixture over turkey; cover and refrigerate 1 hour.
Prepare grill for direct-heat cooking. Grill turkey, 4 inches from the heat, 5 to 6 minutes per side, turning halfway through grilling time. Cook until food thermometer registers 165F in thickest part of tenderloin.
Place on clean serving plate and squeeze lime juice over tenderloins. Slice turkey, crosswise, on the diagonal into 1/4-inch slices.
To prepare the sauce, in a small bowl, combine sour cream, onions, cilantro, chilies, tomato, black pepper and cayenne pepper.
Fill each pita half with turkey and top with cilantro sauce. Add shredded lettuce.