Preheat a chargrill or barbecue hotplate to medium-high. Place sliced mushrooms into a large dish, drizzle with oil. Toss to coat then spoon onto the chargrill or hotplate. Cook for about 2-4 minutes, turning the mushrooms so that they colour evenly.
Sprinkle garlic and chilli over the mushrooms, season well and remove from barbecue onto a large serving platter. Drizzle with vinegar and allow to cool for 1-2 minutes.
Drizzle the mayonnaise over the top of the mushrooms and sprinkle with parsley, serve with char-grilled sourdough bread.