Pat the steak completely dry with paper towels. Mix 1 teaspoon salt, cumin, garlic powder, and oregano in a small bowl. Rub the spice blend all over both sides of the steak, pressing it in so it adheres. Let sit at room temperature for 15 minutes while you prep the toppings.

Heat a large cast iron skillet over high heat until smoking, about 4 minutes. Add the vegetable oil and swirl to coat. Lay the steak in the pan and do not move it. Sear until deeply browned and charred in spots, 4 to 5 minutes per side for medium-rare (internal temperature 130 degrees F). Transfer to a cutting board and let rest for 5 minutes.

Find the direction of the grain (the long muscle fibers running through the meat). Slice thinly across the grain at a 45-degree angle. This is crucial - cutting with the grain makes steak tough and chewy. Season the sliced meat with the remaining 1/2 teaspoon salt.

While the steak rests, warm the tortillas directly over a gas flame for 15 seconds per side until charred and pliable, or in a dry skillet over medium-high heat. Stack and wrap in a clean kitchen towel to keep warm.

Layer 2 to 3 slices of steak onto each warm tortilla. Top with diced onion, a generous pinch of cilantro, and a drizzle of salsa. Serve immediately with lime wedges on the side for squeezing over the top.