Pre-heat oven to 450 degrees and have a medium-sized casserole dish ready. Place prepared pasta in a large bowl and set aside.
Melt butter in a medium sauce pot and gently whisk in flour. Slowly pour in milk and continuously whisk over medium heat until it begins to thicken, about 5-7 minutes. Stir in shredded cheese, pumpkin, grated garlic, salt, pepper, and nutmeg. Whisk mixture until cheese is melted and sauce thickens even further, about 5 more minutes.
Pour pumpkin cheese sauce over the pasta in the bowl and mix until pasta is evenly coated. Stir in plain yogurt and Dijon, then pour entire mixture into baking dish.
Sprinkle bread crumbs, parmesan, and olive oil evenly on top of the pasta then bake uncovered for 20-25 minutes until the contents bubble and the top forms a nice crust.