1 to 1 1/4 lb. flank steak or skirt steak
2 tbsp. neutral-flavored oil (such as peanut or safflower)
Salt and pepper
1 Asian pear or Bosc pear, peeled and coarsely grated
½ red or yellow onion, chopped (about 1 cup)
4 cloves garlic, grated
1-inch piece of fresh ginger, peeled and grated (about 1 tbsp.)
About 1/2 cup beef stock
1 to 2 tbsp. gochujang (Korean red chile paste)
1 tbsp. soy sauce
1 tbsp. Worcestershire sauce
1 scant tbsp. pourable or regular light brown sugar
1 tbsp. toasted sesame oil
4 scallions, chopped
1 small green chile (such as jalapeño), very thinly sliced
2 heads Boston or Bibb lettuce or 3 heads Little Gem lettuce
Sliced seedless cucumbers, toasted sesame seeds, and lime wedges, for serving
Heat a large cast-iron skillet over medium-high to high.
Cut the steak into 4 portions. Thinly slice each piece against the grain into strips that are about 2 1/2 inches long.
Add the neutral oil, two turns of the pan, to the skillet. Add the steaks, arranging in an even layer; cook until browned on the bottom, 2 to 3 minutes. Turn the steaks; season with salt and pepper. Cook for 1 minute more.
Add the pear and onion. Cook, tossing often, until the pear softens, 1 to 2 minutes. Add the garlic and ginger; toss until aromatic, about 1 minute. Mix in the stock, gochujang, soy sauce, Worcestershire, and sugar; simmer until slightly thickened, 2 to 3 minutes. Transfer to a bowl. Drizzle with the sesame oil. Top with the scallions and sliced chile.
Serve the bulgogi with a large platter of cold lettuce leaves. Wrap the meat in the lettuce, then top with the cucumbers and sesame seeds. Serve with the lime wedges.