If the duck is frozen, place it in a deep pan and thaw it in the refrigerator for a few days until it is thawed. Once the duck has thawed, remove it from the packaging and remove everything from inside the cavity.
Place paper towels on top of a large, sturdy cutting board. Place the duck on top of the paper towels and dry the outside with more paper towels. Stuff the cavity with paper towels several times to dry the inside. Use kitchen sheers to trim off the excess fat opposite the cavity opening. Then, use a sharp kitchen knife to score the skin in a criss-cross pattern, taking care not to pierce the meat.
Cut the onion and lemon into quarters. Then, stuff the cavity with one of each at a time, making sure to shove them as far as they will go inside. Then stuff with ⅓ of the fresh rosemary, sage, and thyme. Repeat stuffing with the lemon and onion, alternating with the fresh herbs, ending with the lemon and onion. Fold the "pope's nose" up and wrap the loose skin at the cavity opening around it, then secure the skin with a toothpick. Tie the legs together using kitchen twine in a figure-eight movement.
Line a quarter-sheet pan with paper towels and place a quarter-sheet rack inside. Pat the outside dry with more paper towels and place the duck on the rack. Reserve one teaspoon of Kosher salt for later, and salt the entire outside of the duck with the remaining salt. Cover the duck and place it in the refrigerator for at least eight hours and up to a day to allow for extra crispy skin.
Remove the duck from the refrigerator at least 30 minutes before roasting and preheat oven to 425°F. Place the duck on a plate upside down and remove the paper towels from inside the sheet pan. Line the pan with aluminum foil, spray the rack with non-stick cooking spray, and place back in the pan.
Combine the paprika, garlic powder, black pepper, and reserved Kosher salt in a small bowl. Coat the underside of the duck with half of the spice mixture. Then, place the duck breast side up on the prepared baking pan. Coat the rest of the duck with the remaining spice mixture.
Insert an oven-proof meat thermometer in the thickest part of the duck thigh. Bake in 425°F oven for 15 minutes, then reduce the oven temperature to 350°F and bake for an hour.