Mix mayonnaise with hot chilli sauce in a bowl. Add more chilli sauce if you like it hot.
Slice the tomatoes and red onions and arrange in a dish with the lamb's lettuce.
Preheat the oven to 200 degrees C/400 degrees F (or read instructions on the brioche buns' packet).
Heat a large pan with a generous amount of neutral oil. Turn up the heat to high.
Place the oyster mushrooms in a single layer on the pan, frying just a small part at a time. They should be golden on both sides. This takes about 3-5 minutes. If the pan is dry, add a little extra oil to prevent burning. When the mushrooms are done, transfer them to a dish and fry the next mushrooms in the same way.
When all the mushrooms are golden, return them to the pan and turn down the heat. Add 2-3 peeled, whole garlic cloves and a tablespoon of butter and stir well. When the butter has melted, drizzle the honey over all the mushrooms and stir well.
Season to taste with salt and pepper.
Heat the brioche buns in the oven according to the package instructions.
Serve the burger with chilli mayo on both sides, lamb's lettuce on the bottom, oyster mushrooms, tomatoes and red onion and a slice of cheese (optional).