Dice up the onions, parsley, mint and garlic.
In a bowl, combine all the ingredients with the ground lamb. Mix well to fully combine the egg with the meat.
Divide the meat mixture evenly four ways and press each to form a circular patty.
Cook in a frying pan with a little oil to prevent sticking, or over a BBQ grill. Cook until juices run clear, or no longer pink in the middle.
Serve on a brioche bun with tzatziki, feta, sliced tomato and additional red onion if desired.