In a medium bowl, combine the chopped artichoke hearts, mayonnaise (or Greek yogurt), Dijon mustard, finely chopped shallot, and diced celery if using. Mix in capers or pickles, fresh parsley, and lemon juice. Season with salt and pepper, ensuring it’s well-blended and creamy.

While the filling sits, lightly toast your choice of rustic bread. Place the bread slices in a toaster or on a hot skillet until golden brown, about 3-4 minutes.

Take one slice of the toasted bread and spread a generous layer of the artichoke mixture evenly over it. Optionally, add a layer of fresh lettuce or arugula and sprinkle some cheese. Place another slice of toasted bread on top.

Cut the sandwich in half diagonally for an appetizing presentation. Serve immediately while it's fresh.