When ready to cook, start the Traeger grill on Smoke with the lid open until the fire is established (4 to 5 minutes). Set the temperature to 350 and preheat, lid closed, for 10 to 15 minutes.
In a blender or mini food processor, blend the chiles in adobo until a smooth paste forms. Reserve 2 tablespoons, and save the rest for another use.
Make the chipotle cream: Bring the cream to a simmer in a saucepan on the stovetop over medium heat. Whisk in 1 tablespoon of the chipotle paste, then taste. Add more if you prefer a spicier flavor profile. Stir in the green onions, if using.
Peel the potatoes and submerge them in cold water to prevent them from turning color.
Generously oil a 10- to 12-inch cast iron skillet. Working with one potato at a time, very thinly slice it using the slicing disk of a food processor, a mandolin (slicer), or a sharp knife.
Fan the potato slices in the bottom of the skillet, season with salt and pepper, then top with some of the chipotle cream and the cheese; repeat with the remaining potatoes until you have 4 to 6 layers of potatoes, chipotle cream, and cheese. Cover with foil.
Transfer the skillet to the grill grate and bake the potatoes for 30 minutes. Then, remove the foil to encourage browning.
Continue to bake for another 30 minutes, or until the potatoes are tender and golden brown. At the same time, lay the bacon strips on the grill grate perpendicular to the bars.
Remove the bacon when it is lightly browned and crisp, 20 to 25 minutes. Let cool, then crumble and set aside.
Transfer the scalloped potatoes to a wire cooling rack and let rest for 15 to 20 minutes to firm up. Top with the crumbled bacon and dust with smoked paprika, if desired.