Preheat your Traeger (or similar pellet grill/smoker) to 225°F.

In a large skillet, heat the butter and 1 tablespoon of oil over medium heat. When it glistens, add the sliced onions. Cook for about 5 minutes, stirring occasionally, then add the broth and thyme. Cook for 20-25 minutes or until the onions are caramelized and a deep golden brown. Set aside.

Pat dry the pork loin with a paper towel and place it on a large work surface (baking sheet or cutting board), with the fat cap upright. Use a large knife to make a lengthwise cut down the center of the pork loin, about ⅓ the thickness of the roast. Stop your knife ½" before cutting through to the other side. Open the pork loin up like a book. Starting on the inside left, make the same type of cut lengthwise, again stopping ½" before cutting through the other side. Open it up like a book again to create one large rectangular piece.

Combine the salt, pepper and onion powder in a small dish. Place 1-2 sheets of plastic wrap on top of the pork loin and use a meat mallet to flatten the pork to about ½" thickness. Remove the plastic wrap and season the top of the meat with half of the seasoning mix (reserve the other half for the outside of the roast).

Spread ¾ of the caramelized onions on top of the seasoned pork loin, leaving a ½" to 1" border along the edges of the rectangle. Top the onions with half of the grated cheese.

Starting with the left side (the side that was cut from the center of the roast), gently roll up the pork loin. Secure the entire roast with butcher's twine, tying it in 2-inch intervals.

Rub the remaining 1 teaspoon oil on the outside of the roast and sprinkle it with the rest of the seasoning blend. Set the roast in the smoker, fat cap up. Smoke for about 2 hours or until the internal temperature is 135°F (check it after about 90 minutes).

Increase the heat to 375°F and cook the roast for another 10-15 minutes. During the last 5-10 minutes of cook time, top the roast with the remaining caramelized onions and shredded cheese. The pork is done when the internal temperature is 140°F-145°F. Remove the roast and let it rest for 15 minutes, then slice and serve.