Combine oil, red wine vinegar, sweet chilli sauce and pepper in a screw-top jar. Shake well to combine.
Place mushrooms into a large bowl. Pour 2/3 sweet chilli marinade over mushrooms and stir well to combine. Cover and set aside to marinate for 30 minutes.
Add cherry tomatoes, spring onions, rocket, parsley and remaining marinade to mushroom mixture. Toss gently to combine.