Spray 4-quart slow cooker with cooking spray. In small bowl, mix butter, garlic, 3/4 teaspoon of the salt, the oregano and pepper sauce. Rub mixture onto turkey thighs.
Place onion in slow cooker; top with turkey thighs. Cover; cook on Low heat setting 7 to 9 hours or until turkey pulls apart easily with fork. Meanwhile, in medium bowl, stir together the yogurt, dill, garlic, cucumber and remaining 1/4 teaspoon salt; cover and refrigerate until serving.
Remove turkey from slow cooker; remove from bones. Shred turkey; stir into mixture remaining in slow cooker. Using slotted spoon, divide meat and onion mixture among 6 pita folds. Top with yogurt sauce; pass additional sauce at table.