1. Heat 2 Tbsp. oil in a large skillet over medium-high.
2. Add lamb, cumin, cinnamon, 1 tsp. pepper, and tsp. salt and press into an even layer. Cook, undisturbed, until well browned on the bottom, about 4 minutes. Break up into pieces with a spatula and continue to cook, stirring occasionally, until browned, 12 minutes. Push mixture to one side of skillet and add mushrooms in an even layer; season with salt. Cook, undisturbed, until beginning to brown and soften, 3 minutes, then stir together with lamb mixture. Continue to cook, stirring occasionally, until mushrooms are golden brown, about 2 minutes more.