In a small bowl, combine the ingredients for the dry rub. Set aside. If the cut of beef doesn’t fit into your Dutch oven, cut it into smaller pieces.
Preheat oven to 325 F.
Work the dry rub into all surfaces of the steak well. Swirl a little olive oil into a dutch oven (or any oven-safe stockpot or enameled braiser), heating over medium-high heat until shimmering. Sear the steak on both sides until a dark crust forms, about 3 minutes per side. Transfer the meat to a plate.
Swirl in about ½ tablespoon more oil. Add onions and peppers, stirring to cook for 2-3 minutes. Pour in 1/2 cup stock, stirring to loosen the browned bits on the bottom. Push the vegetables to each side to make room for the steak in the center.
Lay the meat in the pan between the vegetables. Pour in the remaining 1 1/2 cups stock, which should rise to the top of the steak without covering it completely.
Cover the pan with foil, then the lid of the pot. Place in oven, and bake for 2 1/2 hours. Turn off the oven and allow the meat to continue to cook for another 30-60 minutes without opening the lid. (see note 1)
Remove from oven and shred steak in the pan with two forks, being sure to stir the shredded meat and vegetables together in the juices. The meat should essentially fall apart - if it doesn't, put it back in the oven for another 30 minutes.
Serve as a taco or burrito filling or with rice.