In a mixing bowl or salad dressing container: Add shallots and apple cider vinegar. Let sit for about 2 minutes. Add the remaining salad dressing ingredients and whisk until well blended.
In a large mixing bowl: add Brussels sprouts, chopped apple, cooked bacon, chopped walnuts, Pecorino Romano Cheese, spearmint leaves and shallot vinaigrette salad dressing. Mix well.
Optional: adjust with salt/pepper, extra salad dressing, or 1 tablespoon fresh lemon juice for rich and intense flavor.