I cook hamburgers using grass-fed beef two or three times each month. As an alternative, many people make turkey burgers, but when I am in the mood for something different, I use ground lamb. I love lamb's earthy (or slightly gamey, depending on your palate) taste.
To complement the lamb's flavor, I incorporated sautéed onions, chopped parsley and ground cumin into the patties. Another possibility is feta cheese, but I didn't have any.
For a sauce, I felt like something other than ketchup, so I combined equal parts plain whole fat yogurt, mayonnaise and Dijon mustard. Sides were a salad of greens from my garden and pan-fried Japanese sweet potatoes bought at a farmers' market.