In a Dutch oven (or large, deep skillet with a lid), heat the oil over medium-high. Add the onion and eggplant; cook, stirring often, until the onion is light brown and the eggplant softens, about 8 minutes. Add the garlic, oregano and crushed red pepper; cook, stirring constantly, until the garlic is fragrant, about 30 seconds. Add the lamb; season with salt and pepper. Cook, stirring often and breaking up the lamb with a spoon, until the lamb is browned, 2 to 3 minutes. Add the marinara; bring to a boil. Cover and reduce the heat to low. Simmer, stirring the ragu often, until the flavors blend, 5 to 10 minutes.
Meanwhile, bring a large pot of water to a boil. Salt the water, add the pasta and cook to al dente. Reserve 1 cup of the pasta water; drain.
Add the pasta and 1/2 cup of the pasta water to the ragu. Cook, stirring constantly, adding more pasta water if dry, until pasta is coated, about 1 minute.