1. Add lamb through salt and pepper to a slow cooker and cook on high for four hours. Once finished, add flour and simmer on low with the lid off for about 5 minutes or until the juices thicken.
2. Add olive oil and onion to a pan and sauté on low for about 30 minutes, until onions are brown and caramelized. Add brown sugar and stir to combine. Set aside.
3. Toast hamburger bun and add two slices of Castello® Havarti Herbs & Spices on the top and the bottom of the bun. Top with two spoonfuls of the lamb and top with a spoonful of caramelized onions.