Step 1: Prepare the Chicken
If using rotisserie chicken or leftover cooked chicken, shred or dice it into bite-sized pieces. Place the chicken in a medium mixing bowl. If your chicken is dry, this is the perfect opportunity to add moisture through the mayo mixture.

Step 2: Make the Chicken Salad
Add the mayonnaise, finely diced celery, red onion, lemon juice, Dijon mustard, salt, and black pepper to the bowl with the chicken. If using fresh herbs, add them now. Mix everything together thoroughly until the chicken is evenly coated with the creamy dressing. Taste and adjust seasonings as needed – you might want more salt, pepper, or lemon juice depending on your preference.

Step 3: Let It Chill (Optional)
For the best flavor, cover the bowl and refrigerate the chicken salad for at least 30 minutes. This allows the flavors to meld together beautifully. However, if you’re in a hurry, you can proceed directly to assembly.

Step 4: Prepare the Bread
Lay out your bread slices on a clean work surface. If desired, lightly toast the bread for extra texture and to prevent sogginess, though this is entirely optional.

Step 5: Assemble the Sandwiches
Place a lettuce leaf on four slices of bread. This creates a barrier between the moist chicken salad and the bread, keeping everything fresh. Spoon a generous amount of chicken salad (about ½ to ⅔ cup) onto each lettuce-lined slice. Add tomato slices on top of the chicken salad. Top with the remaining bread slices.

Step 6: Slice and Serve
Cut each sandwich in half diagonally or straight across. Serve immediately, or wrap tightly in plastic wrap or parchment paper for lunch boxes and meal prep.