In a small bowl, whisk together the 2 Tbsp. vegetable oil with the soy sauce, chili powder, lime juice, and garlic. To get the most juice out of your lime, microwave it for about 20 seconds before cutting it open.
Place the pork loin in a large zip top bag and pour in the marinade. Squish the mixture around to make sure the loin is completely coated and then refrigerate for one hour or more.
When ready to cook, take the pork loin out of the refrigerator. Preheat the oven to 400 degrees. Heat a large skillet with the remaining 2 Tbsp. of vegetable oil over medium-high heat. When the skillet is very hot and the oil looks wavy on the surface, add the pork loin (do not discard the marinade yet!). Sear both sides of the pork loin until brown and crispy (about 3-5 minutes each side).
After searing both sides of the pork loin, place it on a baking sheet or roasting pan. Baste the loin with the remaining marinade and place it in the oven. Roast for approximately 30 minutes or until the internal temperature reaches 160 degrees. Allow it to rest for 5 minutes before slicing.