1. Prepare the Spice Rub: In a small bowl, whisk together all the spice rub ingredients (chili powder, cumin, kosher salt, garlic powder, onion powder, smoked paprika, black pepper, coriander, and chipotle chili pepper). Set aside the dried oregano for later.
2. Season the Beef: Pat the beef pieces very dry with paper towels. Generously rub the spice mixture all over each piece, pressing gently so it sticks. Save any extra spices for the slow cooker!
3. Sear for Deep Flavor: Heat the vegetable oil in a large cast iron skillet or Dutch oven over medium-high heat until it's very hot. Carefully add the beef in batches (don't overcrowd the pan!) and sear on all sides until beautifully golden brown. This step is key for rich flavor! Transfer the seared beef to a 6-quart (or larger) slow cooker.
4. Add Braising Liquid: Pour the beef broth, salsa, undrained green chilies, tomato paste, lime juice, brown sugar, liquid smoke, beef bouillon, and the reserved dried oregano into the slow cooker with the beef. Stir everything gently to combine.
5. Slow Cook to Perfection: Cover the slow cooker and cook on LOW for 6-8 hours, or on HIGH for 3 ½ – 4 ½ hours. The beef is ready when it's incredibly tender and easily shreds apart with two forks.
6. Shred and Soak: Carefully remove the cooked beef to a rimmed plate or large bowl (keep those delicious juices in the slow cooker!). Using two forks, shred the beef, discarding any large pieces of fat. Return the shredded beef to the slow cooker with the juices and cook on LOW for another 20 minutes. This allows the beef to soak up all the amazing flavors, making it super juicy!
7. Taste and Serve: Taste the shredded beef and adjust seasonings as needed. You might want a little more salt, lime juice, or a dash of hot sauce for an extra kick. Serve this tender, flavorful Mexican shredded beef in tacos, burritos, quesadillas, salads, or burrito bowls!