Preheat the oven to 450 degrees F. Line a roasting pan or baking sheet with aluminum foil and spray it with nonstick spray.
Place the pork on a cutting board and get a sharp knife. I like to slice it twice to open it up so I have a lot of space to work with. I start at the bottom of the pork (about 1/4 inch from the bottom) and slice it lengthwise, then continue to cut again and open up the pork. You want to have a flat surface to work on. I place a piece of plastic wrap over top of the pork and use a meat tenderizer to pound it out to even thickness. Season the inside with salt and pepper. Repeat with the other tenderloin.
Place the pistachios in a food processor and blend until small crumbs remain. In a bowl, combine the pistachios with the ricotta, parmesan cheese, garlic and egg. Add a big pinch of salt and pepper. Stir to combine.
Divide the mixture evenly between the 2 tenderloins. Spread the ricotta mixture on top of the pork, leaving 2 inches or so around the edges so you can roll it up. Sprinkle the chopped herbs on top.
Tightly roll up the tenderloins and tie each with kitchen twine. Season the entire outside with the salt and pepper.
Place the pork on the roasting pan or baking sheet and roast for 30 to 35 minutes, or until the inside is cooked and reads about 140 to 145 degrees F. Let the pork rest for 20 minutes before slicing.