The best burger I have ever had was from a cute little place called Tabor Tavern in Portland Oregon. 1/3 lb. lamb patty, harissa, balsamic onions, feta, arugula, all on a brioche bun. I just checked the menu, and they are still serving it. I have never been quite able to reproduce that flavor, but it opened my mind to how well-spiced lamb is suited to be used in a burger. This flexible sausage recipe can be pumped into links, flattened into patties, or rolled into meatballs.