Adjust oven rack to middle position, place 12-inch cast-iron skillet on rack and heat oven to 500°F Meanwhile, combine cumin, 3/4 teaspoon salt and 1/2 teaspoon pepper in bowl. Cut steak lengthwise with grain into 2 equal pieces, then cut each piece in half crosswise to create four equal pieces. Season steaks with spice mixture and let sit at room temperature.
When oven reaches 500 F, pat steaks dry with paper towels. Using potholders, remove skillet from oven and place over medium-high heat; turn off oven. Being careful of hot skillet handle, add oil and heat until just smoking. Cook steaks, without moving, until lightly browned on first side, about 2 minutes. Flip steaks and continue to cook until lightly browned on second side, about 2 minutes.
Flip steaks, reduce heat to medium-low, and cook, flipping every 2 minutes, until steaks are well browned and meat registers 120 F to 125 F (for medium-rare), 4 to 8 minutes. Transfer steaks to carving board, tent loosely with aluminum foil and let rest while making salsa.
Add corn to now-empty skillet and cook over medium heat, without stirring, until lightly charred, about 4 minutes. Stir corn and continue to cook until tender, about 1 minute; transfer to medium bowl. Stir in onion, jalapeno, lime juice, cilantro, 1/4 teaspoon salt and 1/4 teaspoon pepper. Season with additional salt and pepper to taste. Slice steak thin against grain and serve with tortillas and corn salsa.