Clean, wash and drain the salad. Cut radicchio and lettuce leaves into bite-sized pieces. Clean, wash and thinly slice the mushrooms. Peel and finely chop the onion.
Mix lemon juice and oil. Add onion. Season to taste with sugar, salt and pepper. Mix all salad ingredients with the lemon vinaigrette. Arrange on four plates and garnish as desired with lemon wedges and zests.