Preheat oven to 350 degrees. Spray an uncovered, shallow pan with cooking spray.
Place tenderloin in pan and bake for 20 minutes per pound or until meat thermometer reads 145-150 degrees internal temperature.
Let rest for 10 minutes before making small, ¼ inch slices.
Meanwhile, in a small bowl mix together mustard and mayonnaise to make the sauce. Set aside.
To assemble the sandwiches, layer even amounts of pork, ham, cheese and pickles on 4 slices of the bread.
On the other 4 slices, spread your mustard/mayo sauce.
Place the sandwiches on a panini press coated with cooking spray, or grill them in a frying pan on the stovetop.
Be sure to press down a bit so everything melts together.
Serve immediately.
