Suggested Wine Pairing: Cabernet Sauvignon
Preheat oven to 425 degrees.
Mix ground lamb with paprika, cumin, coriander, dry mustard and fennel seeds. Let lamb sit for 30 minutes to reach room temperature before cooking burgers.
To make the tzatziki sauce, grate cucumber and mix with Greek yogurt, dill, mint and salt and pepper to taste. Set aside in refrigerator until ready to use.
In a nonstick pan, melt butter on low heat and add sliced onions. Let onions caramelize for about 20 minutes stirring occasionally. Once caramelized, set pan aside.
Take the lamb and make 4 even burger patties. On a baking sheet lined with foil, place patties and cook in oven for 15-20 minutes.
While burgers are cooking, start toasting both sides of the buns in the same pan that you caramelized the onions in.
Assemble the burgers: on the bottom half of the bun, place caramelized onions and crumbled feta. Next, add your burger patty and top with tzatziki sauce, lettuce and other half of bun.