Start by chopping the chicken into bite-sized pieces. I find using poached chicken gives a moist, tender texture that works beautifully in this salad.
In a medium bowl, combine chicken, celery, grapes, and almonds. Add mayonnaise, Dijon mustard, lemon juice, salt, and pepper. I mix gently to avoid breaking up the chicken too much.
I like to chill the salad for at least 30 minutes before assembling. This step really lets the flavors meld together and makes the salad even more delicious.
Lay your bread slices flat and add a generous layer of chicken salad. Top with lettuce or spinach if desired. I like pressing the top slice lightly to hold everything together.