1 (11/2-to 134-pound) flank steak, trimmed and cut lengthwise (with grain) into 4 equal pieces
3 tablespoons vegetable oil
1 red onion, three-quarters sliced thin, one-quarter chopped fine
1 poblano chile, stemmed, seeded, and sliced thin
11/2 cups frozen corn, thawed
1 jalapeño chile, stemmed, seeded, and minced
2 tablespoons lime juice
1 tablespoon minced fresh cilantro
12 (6-inch) corn tortillas, warmed
Instructions
Combine cumin, 1 teaspoon salt, and ½ teaspoon pepper in bowl. Pat steak dry with paper towels and season with cumin mixture. Heat 2 tablespoons oil in 12-inch nonstick skillet over medium-high heat until just smoking. Lay steak pieces in skillet, spaced slightly apart, and cook, without moving, until lightly browned on first side, about 3 minutes. Flip steaks and cook until lightly browned on second side, about 3 minutes.
Flip steaks and cook, flipping as needed to ensure even browning, until well browned and meat regis- ters 120 to 125 degrees (for medium-rare), 2 to 3 minutes. Transfer steaks to cutting board, tent loosely with aluminum foil, and let rest.
Heat remaining 1 tablespoon oil in now-empty skillet over medium heat until shimmering. Add sliced onion and poblano and cook, stirring occasionally, until softened and just beginning to brown, 6 to 8 minutes; transfer to bowl.
Add corn to now-empty skillet and cook, without stirring, until lightly charred, about 3 minutes. Stir corn and cook until tender, about 1 minute. Transfer corn to separate bowl and stir in chopped onion, jalapeño, lime juice, cilantro, ½ teaspoon salt, and ½ teaspoon pepper.
Slice steak thinly against grain and serve with warm tortillas, poblano mixture, and corn salsa.