1. In a large pot of boiling salted water, cook pasta according to package instructions. Reserve 1/2 cup pasta water, then drain.
2. Meanwhile, in large skillet, heat 1 Tbsp oil over medium-high. Add sausage and cook, breaking apart with a slotted spoon, until cooked through, about 6 minutes. With slotted spoon, transfer sausage to a bowl and set aside.
3. In same large skillet, add 1 Tbsp oil and bell pepper to skillet and cook, stirring occasionally, until browned in spots, 6 minutes. Add squash and half the tomatoes; cook 1 minute. Add 1/4 cup pasta water, if needed and cook until tomatoes soften, 4 minutes. Return sausage to pan and add remaining tomatoes.
4. Season with red-pepper flakes. Cook until sausage is warmed through and juices thicken slightly, about 2 minutes. Toss with pasta; if necessary, add remaining pasta water to create a light sauce that coats pasta. Serve with Pecorino Romano.