Preheat BBQ for medium-high heat and lightly oil the grill.
Mix the lamb, egg, oregano, sherry, vinegar, chilli flakes, garlic, spring onions, mint, coriander, bread crumbs, salt and pepper together in a mixing bowl with your hands until evenly blended. Form into five patties.
Cook on the preheated BBQ until the burgers are cooked to your desired degree of doneness; about 4 minutes per side for medium-rare. Serve on buns.