Add oil, garlic, onion, spices, chilies, pineapple juice, vinegar, achiote, salt and pepper into a large bowl. Remove and reserve 1/3 cup of marinade.
Add pork and toss. Let marinate for 20 minutes to 2 hours.
When the pork is ready, pre-heat wood fired oven to 400 -500 deg F. (Make a fire in the center of the oven using dry, cured hardwoods, and then when it is going, push it to the back or side of the oven. Continue to feed the fire as needed to keep it at a full flame. Sweep the floor with a copper brush to prepare your cooking surface.)
Slide a cast iron skillet into the oven to preheat. Once preheated, add the pork and pineapple to the skillet and place back into the oven, cooking until pork is done to your preference and pineapple is beginning to brown.
Once pork is done, remove it from the oven and baste with the remaining marinade.
Serve with tortillas, topped with salsa and toppings. Enjoy!