Read all instructions before beginning.
Adjust oven rack to middle position and heat oven to 400°F. Cover a large, rimmed sheet pan with aluminum foil and spray the foil with nonstick cooking spray.
Place the sheet pan in the oven to preheat.
While the oven heats and the pan pre-heats, pat the potato halves dry and place them in a large bowl. Drizzle with olive oil and season with kosher salt and black pepper; stir to coat.
While the oven continues to preheat, prepare the Honey Mustard Sauce; set aside.
When the oven is ready, remove the hot sheet pan and place the potatoes, cut-side down, along both sides of the pan (leave room in the middle for the pork). Return the pan (with the potatoes) to the oven and set the timer for 15 minutes.
While the potatoes cook, pat the pork dry with paper towels and season with salt & pepper. Place the pork on a small sheet pan and rub it all over with the Honey Mustard Sauce: set aside.
Place the sliced onions in the same bowl used for the potatoes and drizzle with olive oil. Season with salt and pepper; set aside.
After the potatoes have roasted for 15 minutes, remove from the oven and place the prepared pork in the center of the pan. Place the onions over and around the potatoes. Place the thyme sprigs over the pork, potatoes & onions and drizzle with olive oil.
Cook 15 minutes, flip the pork over and cook an additional 15-25 minutes or until the internal temperature registers 140°F-145°F (in the thickest part of the pork) on an instant-read thermometer. The total cooking time for the pork is 30-40 minutes.
Remove from the oven, cover with foil, and let rest for 10 minutes. The pork will be slightly pink in the middle and that is exactly what you want.
Before serving, remove any thyme stems.
Serve with a side of Honey Mustard Sauce and Enjoy!