1. Combine the oil, red wine vinegar, mustard, sugar and salt and pepper in a screw-top jar. Shake well to combine.
2. Place the mushrooms in a large bowl. Pour over 1/2 cup of the dressing, toss well to combine. Cover and set aside for 1 hour. Add the cherry tomatoes, capsicum and basil leaves. Pour over the remaining dressing, season with salt and pepper. Toss gently to combine and serve with crusty bread.