Bring a large pot of water to a boil for the pasta.
In a large skillet or Dutch oven, heat the oil, two turns of the pan, over medium- high. When the oil ripples, add the lamb and cook, breaking up with a spoon, until browned, about 5 minutes. Season with salt and pepper. Add the spices; stir until toasted, a minute or so. Add the onion, garlic and thyme. Cover and cook, stirring occasionally, until the onion softens, about 5 minutes. Uncover; add the tomato paste and harissa . Cook, stirring, for 1 minute. Stir in the stock and reduce the heat to low. Let the ragu simmer while you cook the broccoli rabe and the pasta.
In a large skillet, bring 2 to 3 inches of water to a boil for the rabe.
Salt the pasta water. Add the pasta; cook to al dente.
Salt the water for the rabe. Add the rabe; cook 3 to 4 minutes. Drain and chop into bite-size pieces.
Add 1 cup of the pasta water to the ragu; drain the pasta. Toss the pasta with the rabe and half the ragu. Divide among shallow bowls. Top with a little more ragu; garnish with pecorino and mint.