Combine olive oil, minced garlic, ground cumin, smoked paprika, chili powder, fresh lime juice, salt, and pepper in a bowl. Coat the steak well with this marinade. Cover and refrigerate for at least 15 minutes but ideally a few hours or overnight.

In a small bowl, stir together sour cream, chopped cilantro, finely chopped jalapeño, and 1 tablespoon of fresh lime juice. Add salt to taste. Chill until ready to serve.

Heat a cast iron skillet over medium-high heat until smoking slightly. Add the steak and sear for about 4–5 minutes per side for medium rare, depending on thickness. Avoid overcrowding the pan; cook in batches if needed.

Transfer steak to a cutting board and let it rest for 5 minutes. Then slice thinly against the grain.

Warm the corn tortillas in a dry skillet over medium heat for about 30 seconds per side, or wrap in foil and heat in a low oven. Keep warm wrapped in a kitchen towel.

Assemble the tacos by spooning sliced steak onto tortillas, drizzling generously with cilantro lime crema, and topping with pickled red onions and extra cilantro if desired.