To a blender, add the orange juice, vinegar, chili powder, garlic, salt, cumin, paprika, chiles, adobo sauce, chopped onions and chopped pineapple. Blend until smooth. Pour the marinade into a large resealable bag, and add the pork butt and oregano. Refrigerate for at least 4 hours and up to 24 hours.
Preheat the oven to 325 degrees F.
Remove the pork butt from the marinade and set onto a rack set in a roasting pan. Pour the chicken stock into the bottom of the pan and cover the dish with foil. Roast until an internal thermometer reads 185 degrees F, about 4 hours.
Increase the oven temperature to 425 degrees F and cook for an additional 20 minutes to caramelize the pork. Remove from the oven and rest for 20 to 25 minutes.
Meanwhile, preheat a grill to medium-high heat. Brush the pineapple wedges with vegetable oil, grill 2 to 3 minutes per side, and once cool enough to handle chop into a small dice.
When ready to serve, carve the meat into 1/4- to 1/2-inch slices. Serve the pork in warmed corn tortillas; garnish with the remaining finely diced white onion, cilantro, lime wedges, diced grilled pineapple and Roasted Tomatillo Avocado Salsa.
Preheat the oven to 350 degrees F.
Toss the tomatillos with olive oil, season with salt and pepper, and place on a baking sheet. Roast until nicely charred, about 10 minutes. Remove from the oven and set aside to cool.
Combine the tomatillos, 1/4 cup water, cumin, salt, avocado, garlic, jalapenos, onions, lime juice and cilantro in a blender and puree until completely smooth. Place in the refrigerator and allow the sauce to settle before serving.