Mix together minced lamb, onion, mint, garlic, oregano and season generously.
Divide the mixture into fourths and shape into burger patties.
Brush each side with olive oil.
Grill under a high heat, or cook on the barbecue, for 10 to 12 minutes or until golden brown, turning once.
Mushroom Toppers
At the same time as cooking the burgers, cook the mushrooms in a pan with a very small amount of oil for around 10 minutes, turning occasionally, and adding cheese to finish.
Assemble burger and cheesy mushroom in a toasted brioche bun with a dollop of minted mayonnaise.