1For dressing: combine in 3 cup mixing bowl; shallots, mustard, red wine with whisk, slowly pour olive oil in while whisking to make an emulsion then add salt and pepper to taste. Set aside. Whisk again right before you pour over the salad.
2In large bowl combine mushroom, red bell pepper and avocado, drizzle dressing over it and combine gently to prevent breaking the avocados. Transfer to serving bowl and serve immediately. May sprinkle with parsley as garnish.
3If making ahead, remember the avocado will turn brown due to oxidation. Press plastic wrap onto the salad itself to prevent as much oxidation as possible.