Combine all of the ingredients for the burgers in a large bowl and, using your hands, mix until the ingredients are evenly incorporated.
Divide the mixture into 4 evenly sized balls and using your hands for each ball into a patty. Make a small indentation with your thumb in the center of the burger to ensure it cooks evenly.
Preheat the barbecue or a grill pan to medium high heat and once up to temperature, cook the burgers for 4 minutes per side until cooked through (but don't overcook as they dry out).
Prepare the board by laying out the lettuce, sliced red onions and tomatoes, chopped olives, feta, tzatziki and grilled eggplant.