Roast the Pecans: This step is optional but I LOVE the flavor it adds. Preheat the oven to 350 degrees F. Line a baking sheet with parchment paper and spread the pecans out over the parchment. Bake for 9-12 minutes until roasted, turning half way through to prevent burning.
Prepare the Dressing: In a small bowl, combine the mayonnaise, lemon juice, honey, white vinegar, and onion powder. Whisk them together until smooth. Season with salt and pepper according to your taste.
Mix the Chicken Salad: In a large mixing bowl, add the shredded chicken, pecans, grapes, and celery (if using). Pour the dressing over the chicken mixture. Gently stir everything together until all ingredients are well coated with the dressing. Taste and adjust seasoning if necessary.
Toast the Bread or Croissants: While the chicken salad flavors meld, toast the bread slices or croissants lightly if desired. This adds a nice texture and warmth to the sandwich.
Assemble the Sandwiches: Spoon a generous amount of chicken salad onto half of the bread slices or open the croissants and fill them evenly. Top with the remaining slices of bread or the other half of the croissants.
Serve: Cut the sandwiches in half if preferred and serve immediately, or chill in the refrigerator if serving later. This sandwich pairs wonderfully with a side of green salad or your favorite soup for a complete meal.