Begin by cubing the cooked chicken into bite-sized pieces. If you're using rotisserie chicken, simply shred or chop it into cubes.
In a large mixing bowl, add the cubed chicken, chopped celery, halved grapes, cooked peas, mayonnaise, and Dijon mustard. Stir gently to combine.
Add salt and pepper to taste, adjusting the seasoning as needed.
Gently fold in the sliced almonds until evenly distributed throughout the chicken salad.
Take your bread of choice and spread a generous amount of the chicken salad mixture onto one slice. Top with another slice of bread and cut into mini sandwiches.
For best flavor, let the mini sandwiches chill in the refrigerator for at least 30 minutes before serving.
