Gently mix together the ground beef, garlic and salt and pepper in a large bowl.
Lay a large sheet of plastic wrap on your work surface. Tip the ground beef mixture onto the plastic wrap. Using a rolling pin, flatten the ground beef out evenly on the plastic wrap to form a rectangle about ½” thick.
Using a pizza wheel, score the rectangle of ground beef into 16 even-size squares.
Top the 8 squares nearest to you with equal amounts of bacon jam, caramelized onions, and cheddar.
Grasp the edge of the plastic wrap furthest away from you and fold the top 8 burgers over the ones nearest to you.
Peel the plastic wrap off the top of the burgers. Cut through the score marks with the pizza wheel to form 8 square burgers.
With your hands, form each square burger into a round patty, making sure the edges of each burger are sealed to keep the stuffing in. Refrigerate the burgers for at least 1 hour before grilling.
When ready to cook, start the Traeger on Smoke with the lid open until a fire is established (4-5 minutes). Turn temperature to High and preheat, lid closed, for 10 to 15 minutes.
Generously oil the grill grates. Season the burgers with salt and pepper to taste. Grill, turning once, until the internal temperature reaches 160 degrees F, about 12 to 14 minutes.
For the last few minutes of cooking, top the burgers with additional cheese if desired.
Remove the burgers from the grill, tent loosely with foil, and let rest for 5 to 10 minutes before serving.
While the burgers rest, spread the cut sides of the buns with butter. Grill, cut side down, until golden. Assemble the burgers, adding your choice of toppings. Enjoy!