Step 1: Cook the chicken: Poach or roast chicken breasts until fully cooked (internal temperature of 165°F / 74°C). Allow to cool completely, then shred or dice into bite-sized pieces. Ensure the chicken is cool to prevent the mayonnaise from separating.
Step 2: Prepare vegetables: In a large mixing bowl, combine the cooled shredded/diced chicken, finely diced celery, and finely diced red onion.
Step 3: Make the dressing: In a separate small bowl, whisk together the mayonnaise, Dijon mustard, apple cider vinegar, garlic powder, salt, and black pepper until smooth and well combined.
Step 4: Combine ingredients: Pour the prepared dressing over the chicken and vegetable mixture. Gently fold everything together with a spatula or large spoon until all ingredients are evenly coated. Avoid overmixing.
Step 5: Chill and meld flavors: Cover the bowl and refrigerate for at least 30 minutes, or ideally 1-2 hours, to allow the flavors to meld and the salad to chill thoroughly. This step significantly enhances the taste.
Step 6: Adjust and serve: Before serving, give the chicken salad a quick stir. Taste and adjust seasonings as needed. If the salad appears too dry after chilling, add another tablespoon or two of mayonnaise. Garnish with fresh herbs if desired. Serve as sandwiches, lettuce wraps, or with crackers.