How to Make It
Preheat oven to 400°F. In a bowl, toss squash with 2 Tbsp. oil; season with salt and pepper. Spread in a single layer on a baking sheet. Roast, turning often, until tender and lightly browned, 50 to 55 minutes. Add walnuts to sheet 12 minutes before squash is done, then toast.
Warm 2 Tbsp. oil in a skillet over medium heat. Sauté bread crumbs until golden, 7 to 10 minutes. Transfer to a bowl and season with salt and pepper.
Bring a pot of salted water to a boil. Cook spaghetti until al dente, about 10 minutes. Drain, reserving 1/2 cup water. Return pasta to pot over low heat; toss with butter. Stir in squash, nuts, parsley and Parmesan. Toss in 1/2 of the bread crumbs. Add some reserved pasta water if dish seems dry. Divide among 6 plates and sprinkle with remaining bread crumbs.