Preheat your broiler to high heat. Slice the ciabatta bread lengthwise into two long pieces about 1/2-inch thick, creating a top and bottom half. Place both halves cut-side up on a baking sheet. Drizzle the cut sides generously with extra-virgin olive oil, making sure to coat the entire surface evenly. Broil for about 1 minute until the bread is golden and crispy on the edges but still has some give in the center—you want it toasted, not charred.

Remove the toasted bread from the broiler and carefully slide the top half onto a cutting board to cool slightly. On the bottom half still on the baking sheet, spread the red sauce evenly across the toasted surface, leaving about a 1/2-inch border around the edges. Arrange the warm cooked chicken Parmesan cutlets on top of the sauce, overlapping them slightly if needed to cover the bread. I like to warm the sauce ahead of time so it helps heat the chicken through while we're assembling.

Sprinkle the shredded mozzarella cheese evenly over the chicken, making sure to cover all the exposed chicken and sauce. Return the baking sheet to the preheated broiler and broil for 2-3 minutes until the cheese is melted, bubbly, and just beginning to brown on the edges. Watch carefully during this step—broiler intensity varies, so keep your eye on it to prevent burning. The cheese should be golden and slightly crispy on top for the best texture.

Carefully remove the baking sheet from the broiler. Place the toasted top half back onto the bottom half to close the sandwich. Let the sandwich rest for 1 minute—this allows the cheese to set slightly and makes it easier to slice without everything falling apart. I find that this brief rest makes all the difference between a neat slice and a messy one.

Using a serrated knife or bread knife, carefully slice the sandwich into 2-4 portions, depending on how large you want each serving. Cut at a slight angle if you'd like, which creates a more appealing presentation. Transfer to plates and serve immediately while the cheese is still warm and the bread is crispy.