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.
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.