Preheat oven to 425 degrees F. Toss the butternut squash in 2 tablespoons of the olive oil and season with 1/2 teaspoons salt and 1/4 teaspoon ground black pepper. Roast for about 30 minutes, or until soft and somewhat caramelized. Remove from the oven and set aside.
Reduce the heat to 350 degrees F. Slice the tenderloin into three even pieces. Cut away any excess fat from the pork (usually around the outside on a tenderloin).
Season the tenderloin with the remaining salt and black pepper. Add the remaining oil to a large Dutch oven over medium-high heat. When hot add the tenderloin pieces. Brown the tenderloin 6-8 minutes on each side. Remove the pork from the Dutch oven and set aside.
Turn the heat to medium. Add the onion and cook for four minutes or until it softens. Add the garlic and cook for 90 seconds or so. Add the stock to the pan, scrap up any brown pieces stuck to the bottom, and add the tomato paste, paprika, chile powder, and cumin.
Add the pork pieces to the Dutch oven. Cover and place in the oven for about 20 minutes or until done. The FDA recommends you cook pork to an internal temperature of 145 degrees F. as measured by a meat thermometer.
Remove the pork from the Dutch oven and set aside. Place the Dutch oven with the cooking liquid on the stovetop over medium-high heat. Cook so the liquid reduces by about half.
As the liquid is reducing, add the butternut squash to a blender with the heavy cream. Transfer about 4 ounces of the cooking liquid to the blender, too. Carefully blend until smooth.
Use two forks to shred the pork. Add it to a skillet with a one tablespoon of olive oil over medium heat. Cook for 3-4 minutes just to give it a touch of crispiness. Return the shredded port to the cooking liquid. Toss to coat.
One by one, prepare the tacos by adding a few tablespoons of the butternut squash puree down the center of each tortilla, add some shredded pork over it, then sprinkle the Cotija cheese over the top.