In a medium mixing bowl, combine the chopped artichoke hearts, mayonnaise, Dijon mustard, finely chopped shallot, and optional celery. Squeeze in lemon juice and fold in capers or chopped pickles if desired. Season with salt and pepper to taste.

Cover the mixture and refrigerate for at least 15 minutes.

Preheat a non-stick skillet over medium heat. Slice the bread and toast each side until golden brown, about 2-3 minutes per side.

Spread a layer of the artichoke filling on one slice of toasted bread. Layer with greens and optional cheese, then top with another slice of bread.

Cut the sandwich in half and serve immediately.