Spaghetti with Ground Lamb and Spinach

In a large casserole, heat the olive oil over moderately high heat. Add the onion and garlic and cook, stirring, until translucent, about 5 minutes. Add the lamb and cook, stirring, until the meat is lightly browned, about 10 minutes. Stir in the tomato paste, wine and oregano; season with salt and pepper. Cover and simmer over low heat for 10 minutes. Add the spinach and mint and cook, covered, for 10 minutes longer.
Meanwhile, in a large pot of boiling salted water, cook the pasta until al dente. Drain the pasta, reserving 1/4 cup of the cooking liquid. Toss the pasta with the cooking liquid and the ground lamb sauce. Serve at once with the Pecorino cheese.