Remove bones from lamb steaks; discard bones. Cut lamb against the grain into ¼-inch-thick strips. Toss lamb with ground cumin, cornstarch, salt, and 1 tablespoon oil until evenly coated. Let stand at room temperature for 15 minutes.

Bring a large pot of water to a boil over medium-high. Cook noodles according to package directions until al dente. Drain well and set aside.

Heat remaining 2 tablespoons oil in a large skillet or wok over medium-high. Add cumin seeds, if using; cook until fragrant, about 10 seconds. Add lamb in a single layer; cook until browned, 3 to 4 minutes. Stir in onion; cook until lamb is no longer pink and onions are softened and starting to brown, 4 to 6 minutes.

Stir chile crisp, 2 tablespoons water, black vinegar, and dark soy sauce into skillet until well combined. Add noodles; cook, stirring constantly, until noodles are coated in sauce, about 30 seconds. Stir in additional chile crisp to taste. Garnish with torn cilantro and serve immediately.