This chicken salad can be made up to 2 days ahead! Mix ingredients except blueberries and walnuts. When ready to serve, fold in the blueberries and walnuts. Serve on toasted focaccia bread with fresh field greens or in lettuce leaves.
In a large bowl, de-bone and take skin off chicken. Chop meat into bite sized chunks.
Add red onion, mayonnaise, Greek yogurt, celery and mustard powder. Stir until well combined.
Add salt and pepper to taste, stirring each to combine.
Fold in blueberries and walnuts. Serve chilled.