Ingredients

• 1 flank steak (about 1 pound 10 ounces)
• Kosher salt and freshly ground black pepper
• 1 fresh poblano chile
• 1 Fresno chile or red jalapeño
• 1 medium onion, sliced into 1/4"-thick rounds
• 4 tablespoons vegetable oil, divided
• 3 cups (packed) frisée
• 3 tablespoons balsamic vinegar
• 2 teaspoons honey
• Ingredient info: Dark-green poblano chiles are available at better supermarkets and at specialty foods stores and Latin markets.

Instructions

1. Preheat broiler. Line a rimmed baking sheet with foil. Season steak with salt and pepper; set aside.
2. Place chiles and onion on prepared sheet and brush with 2 tablespoons oil. Broil vegetables, turning once, until charred and soft, about 8 minutes. Transfer chiles and onion to a medium bowl and cover with plastic wrap. Let vegetables steam in covered bowl for 10 minutes.
3. Meanwhile, line a platter with the frisèe. Heat remaining 2 tablespoons oil in a large cast-iron or other heavy skillet over medium-high heat. Add steak to skillet and cook, turning once, until browned and cooked to desired doneness, about 10 minutes for medium-rare. Transfer steak to frisée-lined platter; let rest. The heat from the steak will wilt the greens slightly.
4. Peel chiles. Cut in half and remove seeds; cut out core. Finely chop chiles and onion and transfer to a small bowl. Add vinegar and honey to chiles and stir to coat well. Season salsa to taste with salt.
5. Transfer steak to a work surface and thinly slice crosswise against the grain. Return sliced steak to platter, arranging over wilted frisée, and spoon charred pepper salsa over.