Heat 2 tablespoons of vegetable oil in a Dutch oven over medium-high heat. Cook the lamb meat in batches until browned on all sides, using additional oil as necessary, about 3 minutes per batch. Set aside. Heat the remaining 2 tablespoons of vegetable oil in the Dutch oven over medium heat. Stir in the onions; cook until tender and golden brown, about 10 minutes. Add the coriander, cumin, cardamom, ginger, turmeric, garlic powder, black pepper, and cayenne pepper; cook and stir until the spices are fragrant, about 1 minute.