1. Prepare the Marinade: The Flavor Powerhouse
* In a medium-sized bowl, whisk together the freshly squeezed lime juice, orange juice, olive oil, soy sauce (or tamari), and Worcestershire sauce.
* Add the minced garlic, chili powder, ground cumin, smoked paprika, dried oregano, salt, and black pepper. If using, stir in the optional chopped cilantro and diced jalapeño.
* Whisk thoroughly until all the spices are well combined and a cohesive marinade forms. Take a moment to smell it – this is where the magic begins!

2. Marinate the Flank Steak: Time for Infusion
* Place the flank steak in a large zip-top bag or a shallow glass baking dish.
* Pour the prepared marinade over the steak, ensuring it’s well-coated on all sides. If using a bag, press out as much air as possible before sealing. If using a dish, you might need to flip the steak halfway through marinating.
* Marinate in the refrigerator for at least 2 hours, but for best results, aim for 4-8 hours, or even overnight (up to 12 hours is great). The longer it marinates, the more tender and flavorful the meat will become. Do not marinate for more than 24 hours, as the acidity can start to break down the meat too much, resulting in a mushy texture.

3. Optional but Recommended Searing: Building Flavor Depth
* Remove the flank steak from the marinade, letting any excess drip off. Reserve the marinade.
* Heat a tablespoon of olive oil or vegetable oil in a large, heavy-bottomed skillet (cast iron is ideal) over medium-high heat until the oil is shimmering and very hot.
* Carefully place the flank steak in the hot skillet. Sear for 2-3 minutes per side, or until a beautiful brown crust develops. You’re not trying to cook it through, just develop that deep, savory Maillard reaction flavor. Work in batches if your steak is too large for the pan to avoid overcrowding and steaming.
* Once seared, transfer the steak to your slow cooker.

4. Slow Cook to Tender Perfection:
* Pour the reserved marinade over the flank steak in the slow cooker.
* Cover the slow cooker and cook on LOW for 6-8 hours or on HIGH for 3-4 hours. The steak is done when it is exceptionally tender and easily shreds with two forks. Cooking times can vary slightly depending on your slow cooker’s model and the thickness of your steak. Low and slow generally yields the most tender results for flank steak.

5. Shred the Steak: The Grand Finale
* Once cooked, carefully remove the flank steak from the slow cooker and transfer it to a large cutting board or a shallow dish.
* Using two forks, shred the beef. It should pull apart very easily. Shred it against the grain for the most tender pieces.
* Return the shredded beef to the slow cooker and toss it with the cooking juices to keep it moist and absorb even more flavor. Let it sit in the warm juices for at least 10-15 minutes before serving, if possible.

6. Optional Crisping Step (Restaurant-Style Touch):
* For an extra layer of texture reminiscent of carnitas, you can crisp up the shredded beef. Heat a large skillet (you can use the one from searing) over medium-high heat. Add a little of the cooking liquid if the pan is dry.
* Add a portion of the shredded beef in a single layer (don’t overcrowd) and cook for a few minutes without stirring, until the bottom gets a bit crispy. Stir and cook for another minute or two. Repeat in batches if necessary. Alternatively, spread the shredded beef on a baking sheet and broil for 2-4 minutes, watching carefully to prevent burning.

7. Prepare and Warm the Tortillas:
* While the meat is resting or crisping, warm your corn tortillas. This makes them pliable and enhances their flavor.
* Stovetop (preferred): Warm them one or two at a time in a dry skillet (cast iron works best) over medium heat for about 30-60 seconds per side, until they are soft and slightly charred in spots. Keep them warm wrapped in a clean kitchen towel or a tortilla warmer.
* Microwave: Stack a few tortillas, wrap them in a damp paper towel, and microwave for 30-45 seconds until warm and steamy.
* Oven: Wrap a stack of tortillas in foil and warm them in a 300°F (150°C) oven for about 10-15 minutes.

8. Assemble Your Street Tacos:
* Set up a taco bar with the warm shredded flank steak, warmed tortillas, diced onion, chopped cilantro, lime wedges, salsa, and any other desired toppings.
* To assemble each taco, place a generous spoonful of the shredded flank steak onto a warm tortilla (some people like to double up on street taco tortillas for extra durability).
* Top with a sprinkle of diced onion and fresh cilantro.
* Serve immediately with lime wedges for squeezing over the tacos and your favorite salsa on the side.