Using a sheet pan topped with a cast-iron skillet to press the sandwiches is a fun technique that compacts the fillings and results in a neater bite. You can make the chickpea filling a day ahead, but the sandwiches are best assembled and pressed just before serving. Read the labels on condiments and prepared items to make sure they are vegan. Some—like champagne vinegar and Dijon mustard—can be not-so-obvious sources of animal products.