Combine the olive oil, balsamic vinegar, garlic, brown sugar, sweet chilli sauce and pepper in a screw-top jar. Shake well to combine.
Place mushrooms into a large bowl and pour over the vinegar mixture. Toss well to combine.
Spoon the mushrooms and marinade into a baking dish lined with non-stick baking paper. Roast for 15 minutes or until tender, tossing once or twice. Sprinkle with fresh herbs.