In a small bowl, whisk together ingredients for the Samurai sauce. You can add more sambal oelek if you want it spicier, but start with the 3 tsp because it has a good kick!

Cut the loaf of ciabatta in half horizontally. Begin by layering the hand torn chicken on the bottom half of the loaf. Top with cheddar cheese in a thick layer, followed by thick layers of red onion and spinach.

Spread the sauce on the top half of the ciabatta loaf and top the sandwich off.

Wrap the sandwich loaf tightly with plastic wrap. Place on a plate or sheet pan large enough for the sandwich to lay flat.

Add the plate to the refrigerator and place a heavy skillet large enough to cover the entire sandwich on top. Let press in the refrigerator for at least 6 hours (it's better if you do it overnight).

When ready to serve or pack up for a picnic, trim the sides of the sandwich to form a rectangle. Cut the rectangle into four sandwiches (approximate size shown in pictures above). Serve immediately or chill until ready to eat.