Whisk together 1 cup of mayonnaise, pepper, garlic powder, and celery salt until combined. Combine the chicken, celery, cranberries, and cashews in a large bowl. Pour the mayonnaise mixture over the chicken mixture and stir until evenly combined.
Spread 1/2 tablespoon of mayonnaise on each slice of toasted bread. Divide the chicken salad between four of the slices of toast; top each with a lettuce leaf and a slice of tomato. Complete each sandwich with the remaining toast slices.