Cook sausage, mushrooms, onion, squash, sage, and garlic in a large skillet over medium-high, stirring often, until sausage is cooked through and crumbled, 8 to 9 minutes. Add wine; cook until almost absorbed, 1 to 2 minutes.

Meanwhile, cook pasta in a large pot of boiling water 4 minutes, or to desired degree of doneness. Drain.

Stir stock into sauce; bring to a boil. Reduce heat to medium; cook 1 minute. Stir in pasta, cream, 1/4 teaspoon salt, and 1/4 teaspoon pepper. Cook until heated through, 1 to 2 minutes.

Stir together parsley, pepitas, cheese, zest, remaining 1/4 teaspoon salt, and remaining 1/4 teaspoon pepper in a small bowl. Divide pasta among 4 bowls; top with parsley mixture.