Pork Belly: Combine salt, sugar, and black pepper. Rub pork belly with mixture and coat evenly. Let sit covered in the fridge overnight.
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 High and preheat, lid closed, for 10 to 15 minutes.
Place the pork belly in a roasting pan and place pan on the grill. Cook on High for 30 minutes until a little bit of color has developed. Reduce heat to 250 degrees F and continue to cook for 1-2 hours or until pork belly is tender.
Let the pork belly cool at room temperature. When cooled enough to handle, wrap in plastic and let cool in the refrigerator until chilled (at least a couple of hours).
Mac & Cheese: Bring a large pot of salted water to a boil. Add the noodles and cook until tender. Drain and reserve. Heat another large sauce pan over medium high heat. Add olive oil, butter, and onion. Sauté until tender.
Once onion is tender, add garlic and sauté until fragrant. Sprinkle in flour and stir. Cook roux until flour smells like popcorn and has turned a golden color.
While whisking, stir in the whole milk. Make sure to work out any lumps. Simmer on medium heat until mixture has thickened. Remove from heat and stir in cheese, nutmeg, and cayenne. Add in noodles and stir to combine.
Cut pork belly into good sized chunks or slices and heat on the grill just enough to warm through.
To serve spoon mac and cheese into a bowl and top with pork belly. Enjoy!