The herb mayonnaise with dill, tarragon and basil really adds a lot of flavor to a simple sandwich that has crunchy lettuce, smooth avocado and cold chicken.
Toast the bread while you fix everything else.
Mix the mayonnaise with the dill, tarragon and basil.
Spread the herb mayonnaise on the toast.
Add the lettuce, onion, avocado and sliced chicken to one piece of toast and top with the other.