Using a sharp chef’s knife, slice the meat into 1/4” inch thick slices. Transfer to a large bowl.
Place ancho and guajillo chilies in a large saucepan over medium high heat and cook turning chilies occasionally, until puffed, and lightly browned (about 5 minutes). Add chicken stock then pour contents of pan into a small bowl. Cover with plastic wrap and set aside.
Wipe out saucepan, add oil, and return to medium-high heat. Add cumin and oregano and cook until aromatic (about 30 seconds).
Add chipotle chiles and sauce and cook about 30 seconds longer. Add vinegar, orange juice, salt, and sugar. Remove from heat.
Coarsely chop 1 onion half. Coarsely chop 2 pineapple rounds, discarding core. Cover and chill remaining pineapple.
Place chopped onion and chopped pineapple in blender. Add chiles and stock and chipotle mixture and blend until smooth. Pour marinade over pork and mix until pork is evenly coated. Layer the marinated meat into an empty quart-sized container and marinate in the fridge for 2-3 hours max.
Remove from the fridge and thread the meat slices onto a skewer right down the middle of the meat. When the skewer is full, top the stack with the reserved pineapple top and build a base from the pineapple bottom sticking the skewer into the bottom. The whole thing should stand up right.
When ready to cook, start the Traeger grill on Smoke with lid open until fire is established (4 to 5 minutes). Set the temperature to 275 degrees and preheat, lid closed, for 10 minutes.
Place the pineapple pork tower upright in the center of the grill and cook until the internal temperature reaches 185 degrees F (about 4 hours).
Grill remaining pineapple until warm and slightly charred (4-6 minutes per side). Transfer pineapple and pork to work surface. Chop pineapple into 1/2-inch cubes. Chop pork. Transfer to platter and toss pineapple and pork to combine.
Finely chop remaining onion half and place in medium bowl. Add cilantro and toss to combine. Grill tortillas until warm and slightly charred, about 10 seconds per side.
Serve pork-pineapple mixture with onion-cilantro relish, warm tortillas and lime wedges. Enjoy!