Use a sharp knife to slice 2-3 pounds boneless pork butt roast into thin ¼-inch slices. Place slices in a large mixing bowl or resealable plastic bag.
Peel, core, and cut 1 large fresh pineapple into 2-inch wide spears. Dice approximately 1 cup of pineapple and set the rest of the spears aside.
Roughly chop 1 medium white onion and add it to a blender along with the 1 cup of diced pineapple. Add in ½ cup orange juice, ¼ cup distilled white vinegar, 2 tablespoons ancho chili powder, 4 cloves garlic, 1 chipotle in adobo pepper, 1 ½ teaspoons salt, and 1 teaspoon dried Mexican oregano. Blend until smooth, about 60 to 90 seconds.
Pour marinade over pork and toss to coat the meat. Cover the bowl with a lid or plastic wrap and refrigerate 4 hours to marinate.
Heat a large heavy skillet or grill to high heat. Working in small batches, sear each slice of pork until cooked through, 2 to 4 minutes. At the same time, grill pineapple until lightly charred.
Roughly chop the cooked pork and dice cooked pineapple. Serve meat up hot on a warmed tortilla topped with freshly chopped cilantro, diced grilled pineapple, slicdiced onion, and a lime wedge for squeezing.
