Gently lay out a collard leaf on a dry cutting board, stem end facing away from you. Divide the turkey mixture into eight portions. Place one portion of turkey near the stem end of the leaf. Fold in the side edges of the leaf and roll up the collard around the filling, like a burrito. Place the collard roll in the casserole dish, seam side down. Repeat with the rest of the collards and filling. Drizzle barbecue sauce over the top of the rolls, cover with aluminum foil and place in the oven. Bake for about 30 to 40 minutes until the collard rolls are tender. Serve warm.