Preheat the oven to 350 degrees F.
Heat the olive oil in a heavy-bottomed pot over medium heat. Add the garlic, onion, fennel, and fennel seeds. Cook until the onions start to become translucent.
Add the sausage and cook through, crumbling as it cooks. Once cooked through, remove the pot from the heat.
Cook the pasta according to directions on the package. Drain and set aside.
Add the pumpkin, Greek yogurt, heavy cream, spices, and parmesan cheese to a medium-sized bowl. Whisk to combine.
Add pasta to the pot with the vegetables and sausage. Add the pumpkin sauce and stir until the pasta and sausage are coated.
Pour the pasta into a 9x13-inch baking dish. Top with shredded mozzarella.
Bake for 20 minutes, or until the sauce is bubbly and the mozzarella has melted.