First you will need to roll-cut the pork roast to open it up for stuffing. You can either have your butcher do it or you can do it at home. To roll cut the roast, remove any strings around the pork roast and then lay the roast on a cutting board, with a shorter side facing you. With a sharp knife make an incision along the length of the meat parallel to the cutting board, one-third of the way up the height of the meat, as if you were using the knife to open a book. Cut into the meat, gently pulling it back as you cut, making sure not to cut all the way through. Once done, spread the cut meat until it looks like an open book, with the side on the left thicker than the other.
With the meat now open, place the knife at the top of the center crease or "spine" and cut along the length of the meat parallel to the cutting board, like you did for the first cut, this time halfway up the height of the crease, again pulling back as you cut. At this point, as the meat opens it will be more like unrolling a roll of paper towels. Continue to cut in and unroll until you've reached the end and the meat is flat. Cover the flattened meat with plastic wrap and then gently pound with the flat side of a meat mallet until the meat is 1/2 inch thick, if it's not already. If it's not a perfect rectangle, that's okay.
Preheat the oven to 350 degrees F. Line a roasting pan with aluminum foil.
To make the jalapeno pesto, combine the jalapenos, cilantro, garlic, pecans cumin, 2 tablespoons of the Cotija cheese, 3 tablespoons of the olive oil and the lemon juice in a blender or food processor and blend until smooth, scraping down the sides as you blend, if necessary. Add salt and black pepper to taste.
Spread the jalapeno pesto in the center of the flattened pork loin, leaving a 1/2 inch border around the edges, and then sprinkle on top of the pesto the remaining 2 tablespoons cheese. Starting from the short end, roll the pork roast and then secure with kitchen string at one-inch intervals. Rub the outside of the rolled roast with the remaining 1 tablespoons olive oil and sprinkle lightly with salt and pepper (and if any pesto oozed out of the roast as you rolled, you can rub it over the outside, too).
Roast, uncovered, for 40-45 minutes, or until a meat thermometer reads 145 degrees F. Allow the roast to rest for 15 minutes before slicing and serving (there will be carry-over cooking).