Step 1: Toast the Walnuts - Preheat your oven to 180°C (350°F). Spread the walnuts in a single layer on a baking sheet and toast them for about 5 minutes or until they are fragrant and lightly golden. Allow them to cool for a few minutes before chopping them roughly.

Step 2: Prepare the Ingredients - Cube the poached chicken breasts into bite-sized pieces. Core and chop the red and green apples into small cubes. Slice the celery thinly and chop the parsley.

Step 3: Combine the Salad Ingredients - In a large mixing bowl, combine the cubed chicken, chopped apples, sliced celery, and raisins or grapes. Gently fold these ingredients together.

Step 4: Make the Dressing - In a separate bowl, mix together the low-fat mayonnaise, fresh lemon juice, and Dijon mustard until well combined.

Step 5: Combine Salad and Dressing - Pour the dressing over the salad mixture and toss everything together until all the ingredients are nicely coated.

Step 6: Let the Salad Rest - Allow the Chicken Waldorf Salad to rest for about 10 minutes at room temperature.

Step 7: Prepare the Lettuce Base - Rinse and dry the romaine or gem lettuce leaves thoroughly, then arrange them on a large serving platter.

Step 8: Serve and Enjoy - Scoop the Chicken Waldorf Salad onto the prepared lettuce leaves and enjoy!