Preheat oven to 400°F.

Toss pumpkin with olive oil and arrange on sheet pan in a single layer. Roast 20 to 25 minutes at 400°F, until tender when pierced with a fork.

While pumpkin is roasting, cook fettuccine according to package directions. Drain, but do not rinse; set aside.

Transfer pumpkin to a food processor and add stock, cream cheese, garlic, salt, and nutmeg. Process until smooth, adding additional stock if desired. 

Transfer pumpkin sauce to a small saucepan and heat over low heat until warm.

Toss cooked pasta with sauce and divide among plates. 

Garnish with walnuts.