Preheat the oven to 400 degrees Fahrenheit.
Heat a large ovenproof skillet over medium-high heat. Add one tablespoon of grape seed oil to the pan. Season the pork tenderloin with ½ teaspoon salt and black pepper. Add the pork to the pan and cook for 4 minutes. Turn pork over, cook 2 additional minutes.
Cover the pan with foil and bake the pork for 5 minutes. Then, uncover and cook for an additional 5 minutes. Remove the pork from the oven. Place the pork on a cutting board and let it rest for 10 minutes.
While the pork rest prepare the gravy. In a bowl, mix together the turkey stock, cornstarch, cider vinegar, and ½ teaspoon salt. Then add to the skillet. Let it reduce down until thick (about 5 minutes on medium heat). Once the gravy is done. Remove from the skillet, pour in a bowl, and set to the side.
Place the skillet back on the stove top. Add in the grape seed oil, minced garlic, and bell peppers. Cook for 5 minutes on medium heat. Then place in the oven for 5 minutes. Remove from the oven, slice pork, divide evenly among plates between pork and peppers. Pour gravy on top of pork and enjoy immediately.