Heat the vegetable oil in a large skillet over medium-high heat. Season the beef with the cumin, 1 teaspoon salt and 1/4 teaspoon pepper. Add to the skillet and cook until golden brown, about 3 minutes per side.
Transfer the meat to a 6-quart slow cooker, then add the salsa, onion and garlic. Cover and cook on high, 6 hours.
Remove the meat to a cutting board and shred with 2 forks, discarding the excess fat. Return the meat to the slow cooker and stir in the cilantro.
Serve the meat in tortillas and top as desired. Serve with lime wedges.
Photograph by Christopher Testani
Courtesy of Food Network Magazine