Season pork loin with garlic powder, salt and pepper. Heat grapeseed oil over medium-high heat in a large skillet. When the oil begins to shimmer, sear the pork on all sides. Transfer the meat to the oven, cover and let roast until fork tender and to an internal temperature of 162 degrees F on an instant-read thermometer, about 40 minutes. In last 10 minutes of roasting time increase heat to 425 degrees F and remove cover. Remove from oven to let carryover cook to 170 degrees F. Slice after meat has rested.