Using a food processor, pulse the mushrooms until they are very finely chopped. In a large saucepan sauté the mushrooms in a drizzle of olive oil. Sauté until the mushrooms are fully cooked and have lost most of their liquid, 10-12 min. Set aside to cool.
In a large bowl combine the remaining ingredients and the cooled, cooked mushrooms. Form into 6 equally sized patties.
In a hot cast iron pan or on the braai, cook the patties until golden brown on both sides and fully cooked through. 10-12 minutes.
Assemble burgers with all your favourite fixings and serve warm.