Arrange onion slices in a single layer at the bottom of the slow cooker crock and place the flank steak on top. We used two pounds of flank steak and cut it into four pieces for quicker, even cooking.
Then make the zesty marinade to flavor your steak (this is the real star of the show). Mix lime juice, vegetable oil, apple cider vinegar, garlic, chili powder, cumin, paprika and smoked paprika, salt, pepper, and ancho chili powder. Pour the spicy mixture over the flank steak in the slow cooker crock.
Cover the slow cooker and cook on HIGH for 2 to 3 hours or on LOW for 5 to 6 hours.
When the steak is fully cooked, remove it and shred the meat - reserving the juices. Transfer the steak back to the slow cooker and spoon the marinade back over top to moisten and flavor before serving. Add a little garnish of cilantro and a squeeze of fresh lime juice to complete the dish.
Serve this slow cooker carne asada as a taco filling on Taco Tuesday or use it to make loaded nachos and feed the fans at your house on gameday. Making carne asada in the slow cooker is also a great meal prep option for the week. Store it in the fridge to quickly throw into quesadillas, burrito bowls, or to stir into macaroni and cheese throughout the week.
Prefer the grill, even on chilly fall nights? Use the same marinade for your grilled carne asada and enjoy tasty grilled carne asada all year long.