In a slow cooker place the pork tenderloin. Season the pork with salt and pepper.
Add the Italian seasoning, fennel seeds, bay leaf, onion, and green pepper.
Add water, enough to cover the ingredients.
Cook the pork for 4 hours on high (I used a 2-quart slow cooker, so if using a large slow cooker cooking time may vary).
Remove the pork from the slow cooker and shred. Return the pork to the slow cooker and continue to cook for another 1 1/2 hours to 2 hours.
To assemble the sandwiches-
Slice the bun/roll. Place the Italian pork on bottom of the roll. Place the mozzarella over the top of the pork. Add the green peppers and onions over the cheese.
Place the sandwiches on a baking pan and place in an oven that has been preheated to 300 degrees F. Heat until the cheese is melted.