Set the Ninja Woodfire Grill to the Smoker function, add wood pellets, and preheat to 225°F (107°C).
Trim the silver skin and excess fat from the pork tenderloin, then pat it completely dry with paper towels.
In a small bowl, combine the garlic powder, onion powder, paprika, salt, black pepper, brown sugar, thyme, and mustard powder.
Rub the tenderloin all over with olive oil, then coat generously with the spice mixture, pressing it into the meat.
Place the tenderloin on the grill grate and close the lid. Smoke at 225°F for 1.5 to 2 hours, until the internal temperature reaches 145°F (63°C).
(Optional) For grilled-style edges, switch to the Grill function on high and sear 2–3 minutes, turning once.
Rest the pork 5–10 minutes, then slice into medallions and serve.