In a medium mixing bowl, combine the chopped artichoke hearts, mayonnaise, Dijon mustard, and finely chopped shallot. Add in any optional ingredients like celery, capers, and fresh parsley. Drizzle with lemon juice, then season with salt and pepper to taste. Mix thoroughly until all ingredients are well combined and creamy.

Preheat a skillet or griddle over medium heat. Lightly toast each slice of rustic bread for about 2-3 minutes on each side until golden brown. Set aside.

On one slice of the toasted bread, generously spread a layer of the creamy artichoke filling. Top it with fresh lettuce or arugula. If desired, layer cheese over the greens, then place a second slice of toasted bread on top.

Carefully cut the sandwich in half or quarters. Serve immediately to enjoy the textures of the crunchy bread and creamy filling.