Pork would be really good for this also. I used this for tacos but it would be great for burritos.
1 (4 pound) chuck roast
1 teaspoon salt
1 teaspoon ground black pepper
2 tablespoons olive oil
1 large onion, chopped
1 teaspoon chili powder
1 teaspoon Cumin
1 teaspoon ground cayenne pepper
1/4 bottle hot pepper sauce
1 teaspoon garlic powder
Trim the roast of any excess fat, and season with salt and pepper. Heat olive oil in a large skillet over medium-high heat. Place meat in hot skillet, and brown meat quickly on all sides.
Transfer the roast to a slow cooker, and put onion over meat. Season with chili powder, cayenne pepper, hot pepper sauce, and garlic powder and cumin. Add enough water to cover 1/3 of the roast.
Cover, and cook on High for 6 hours, checking to make sure there is always at least a small amount of liquid in the bottom. Reduce heat to Low, and continue cooking for 2 to 4 hours, or until meat is totally tender and falls apart and then I would leave it in the broth for at least another hour cooking on low.