2.Heat 1 tablespoon oil in a large frying pan over moderate heat. Cook and turn sausages for 5 minutes or until cooked. Transfer to a heatproof plate. Cool; slice thinly.
3.Add onion to pan; cook and stir for 5 minutes or until soft. Remove from heat. Add sausage, parsley, breadcrumbs and feta to onion. Season with pepper.
4.Arrange mushrooms, stem-side up, on a baking tray. Spoon feta mixture onto mushrooms. Bake for 10-12 minutes or until mushrooms are tender.
5.Combine beetroot, rocket and walnuts in a large bowl. Drizzle with remaining oil and the vinegar; toss gently to coat. Place mushrooms on serving plates.