In a small bowl combine dried cranberries and enough boiling water to cover. Let stand for 10 minutes; drain well.
In a large bowl combine cranberries, walnuts, bread crumbs, rosemary, salt, and pepper. Add ground chicken; mix well. Shape mixture into six 3/4-inch-thick patties.
For a charcoal or gas grill, grease grill rack. Place patties on the rack of a covered grill directly over medium heat. Grill for 14 to 18 minutes or until no longer pink (165 degrees F), turning once halfway through grilling and topping patties with cheese for the last 2 to 3 minutes of grilling.
If desired, spread bottoms of rolls with mayonnaise; top with spinach. Add burgers and, if desired, red onion. Replace tops of rolls.