Prepare the chicken: If using rotisserie chicken, remove meat from bones and discard skin. Chop into bite-sized cubes or shred using two forks. Place in a large mixing bowl.
Chop the vegetables: Dice celery into small pieces. Slice green onions thin. Halve the grapes. Add all to the bowl with chicken.
Make the dressing: In a small bowl, whisk together mayonnaise, Dijon mustard, lemon juice, salt, and black pepper until smooth and creamy.
Combine everything: Add sliced almonds to the chicken mixture. Pour dressing over everything. Gently fold with a large spoon until all ingredients are evenly coated.
Add fresh herbs: Sprinkle chopped parsley (or your choice of fresh herbs) over the salad. Give it one final gentle mix.
Chill: Cover the bowl and refrigerate for at least 20-30 minutes. This allows flavors to blend together.
Taste and adjust: Before serving, taste the salad. Add more salt, pepper, or a squeeze of lemon if needed. If it seems dry, stir in another tablespoon of mayo.
Serve: Enjoy in sandwiches, wraps, lettuce cups, or on its own as a protein-rich salad.