Line a crock pot with slightly warmed banana leaves (pop them in a warm oven for 10 seconds or run them over a flame on a gas stove, the heat makes them more flexible).
Place pork shoulder on top of banana leaves and cover with more banana leaves, making sure to tuck leaves around the sides. Cook for 7 hours on low setting.
Slice red onion and 3 habanero peppers (or to taste), mix with fresh squeezed lime juice, marinate in fridge.
About 1 hour before the meat is done, squeeze the bitter oranges and blend the juice with the achiote paste in a food processor. Add the garlic (raw and peeled) and three habanero peppers. Blend.
In a large stock pot over low heat, combine orange juice achiote mixture with chicken stock and fresh squeezed orange juice. Let simmer for 30-40 minutes. Salt to taste.
When the meat is cooked, shred and add to the sauce, letting the sauce and meat simmer together for another 30 minutes.
Serve with warm tortillas, onions, and peppers.