To prepare red onion relish: Mix 1 cup vinegar with 1 cup water and heat in saucepan with bay leaves. Add the onion and boil for ten minutes. Remove from heat and let cool before refrigerating. This will be served cool.
In a glass or ceramic bowl mix remaining vinegar, 1-1/2 c. hot water and the bouillon powder. Dissolve the achiote paste tablet in the mixture.
Cut excess fat from pork and cut it into large chunks. Add pork to the achiote paste sauce in a pressure cooker or large pot with cover. Bring to a boil, then reduce heat and cook until meat is tender and comes apart with a fork, adding water if needed to keep the meat mixture covered.
When cooked well, pull the meat apart and serve in a large bowl with red onion relish on the side. Serve with warm corn tortillas and fresh salsa and let people make their own tacos. A nice, fresh salad makes this a complete meal.