How to Make It
Cook the pasta according to the package directions. Reserve ½ cup of the cooking water; drain the pasta and return it to the pot.
Meanwhile, heat 2 tablespoons of the oil in a large skillet over medium heat. Add the bread crumbs and cook, stirring often, until golden brown, 2 to 3 minutes. Mix in the thyme and ¼ teaspoon each salt and pepper; transfer to a small bowl. Wipe out the skillet.
Heat the remaining tablespoon of oil in the skillet over medium-high heat. Add the sausage and onion and cook, breaking up the sausage with a spoon, until the onion is soft and the sausage is browned and cooked through, 8 to 10 minutes.
Add the sausage mixture, arugula, and ¼ cup of the reserved cooking water to the pasta and toss to combine (add more cooking water as needed to loosen the sauce). Serve sprinkled with the bread crumbs.