Remove stems and seeds from chili pods by tearing off stems, and ripping pod open with thumb; shake seeds out.
Peel onion and chop into quarters.
Smash and peel garlic cloves.
Add chilies, onion, garlic, cumin, paprika, oregano and chicken stock to a sauce pan and simmer on medium high heat for about 10-15 minutes until chilies are soft. Set aside to cool slightly.
Puree chilies and stock mixture until smooth.
Salt and pepper all sides of the beef roast.
In a dutch oven on medium high heat, sear all sides of the roast until a dark crust forms. You don't need to use oil here.
Pour pureed chili mixture over seared beef.
Pour in additional liquid such as stock, beer, ginger ale or water and add bay leaves. Squeeze the juice of a lime over everything.
Cover meat loosely with foil or lid, and cook at 275 degrees for 5-7 hours until fall apart tender. Occasionally spoon or baste liquid over meat.
Use two forks, dull knives, or metal spatula to chunk the meat up into small pieces. Toss with remaining liquid in pan.
Serve on corn tortillas with minced onion, fresh cilantro and lime wedges.