In a large pot of boiling salted water, cook pasta until al dente. Reserve 1/2 cup pasta water; drain pasta, and return to pot. Add butter, cheese, and pasta water; toss until butter has melted.
Gently fold in roasted pumpkin; season with salt and pepper. Divide among serving bowls, and serve immediately.
Sugar pumpkins are members of the gourd family; find them at farmers' markets or supermarkets. Choose smooth, deep-orange pumpkins that are heavy for their size, without cracks or soft spots. Store in the pantry for up to one month.