Remove bones from lamb steaks; discard bones. Cut lamb against the grain into ¼-inch-thick strips. Toss together lamb, ground cumin, cornstarch, salt, and 1 tablespoon oil in a medium bowl until lamb is evenly coated. Let stand at room temperature for 15 minutes.
Meanwhile, 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, stirring often, until fragrant, about 10 seconds. Add lamb in a single layer; cook, undisturbed, until well browned, 3 to 4 minutes. Stir in onion; cook, stirring occasionally, 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 well coated in sauce, about 30 seconds. Stir in additional chile crisp to taste. Garnish with torn cilantro, and serve immediately.
