3 chiles (Thai, serrano, or jalapeño), thinly sliced into rounds
¼ cup tamarind concentrate
3 tablespoons light brown sugar
1 tablespoon kosher salt
1 tablespoon vegetable oil, plus 4 tsp more for cooking
1½ pound hanger steak, de-membraned and cut into 4 pieces

Whisk chiles, tamarind, brown sugar, salt, and 1 Tbsp. oil in a shallow baking dish until sugar is dissolved. Add steak and turn to coat. Cover and chill at least 4 hours, or up to a day.