Bring the vegetable stock to the boil with the lentils and cook until the lentils are tender; about 35 minutes. Drain, reserve the stock.
In a food processor combine onion, garlic and olives, pulse until in finely chopped. Add the cooked lentils then pulse until combined. Add the olive oil and feta, then pulse to combine.
Turn mixture into a bowl and add the breadcrumbs, wheatgerm and diced coriander. Season to taste. Form into burger shapes. If the burgers are too dry and cracking add some of the reserved stock to moisten.
Heat a frypan to moderate heat then add some oil. Cook burger until brown then turn to cook the other side. They are a little delicate so turn with care.