Preheat the oven to 375F.

Butterfly the pork by slicing it down one of the long sides, but stopping before you slice all the way through. Open it out. Use a meat tenderizer or similar to pound the meat until it has an equal thickness of about ½" all over. Set aside.

Add the herbs and olive oil to a mini food processor and blend until a loose paste has formed. Spread it onto the pork. 

Next, place slices of fresh mozzarella down the center.  Season with salt and pepper, then roll up the pork, securing it in place with kitchen twine at several intervals. 

Place the tenderloin seam-side-up on a baking sheet, season with salt and pepper, and roast in a preheated oven until the thickest part of the meat (not the filling!) has reached 145F. A meat thermometer is recommended  - and check the temperature in several areas to ensure that it is fully cooked.

Leave to rest for 5 minutes, then slice and serve.