Build the sandwich: Slice bread loaf in half horizontally. Spread half of the pesto (2 tablespoons) on each side of the bread loaf. Next, layer the sliced chicken on the bottom half of the loaf. Follow this with the spinach leaves, any optional toppings you like, and then the provolone cheese slices. Place the top of the loaf onto the sandwich.

Wrap the sandwich: Use plastic wrap or parchment paper and rubber bands to wrap the entire sandwich securely.

Press the sandwich: Place the wrapped sandwich on a secure shelf in the fridge. Place a cutting board on top of the sandwich, and then place a heavy weight on the cutting board (helps distribute the weight). You can use a cast iron pan, a brick, books, or anything else you can find. Press for at least 4 hours, up to overnight (12 hours).

Serve the sandwich: Once the sandwich is pressed, slice vertically into 4-6 individual sandwiches. Serve immediately or wrap up the sandwiches and save for a to-go or picnic lunch. Refrigerate and enjoy within 2-3 days.