Heat oil in nonstick pan over medium heat. Add shallots; cook until transparent. Add mushrooms; cook 3 minutes, stirring. Add parsley and lemon juice. Season to taste with salt and pepper. Remove from heat. Stir in turkey.
Tear or cut radicchio into small pieces and use to line a serving platter. Top with turkey and mushroom mixture. Cut plums into thin slices and add to salad.
To make cheese dressing, beat cheese, 3 tablespoons milk and vinegar in a bowl until well combined. If mixture is not sufficiently runny, add remaining 1 tablespoon milk. Add salt and pepper to taste. Drizzle dressing over salad. Garnish with walnuts.
If plums are not in season, use fresh fruits, such as apricots or pears. Pecans, blanched almonds or pistachios or a mixture of nuts may be used in place of walnuts.