Heat olive oil in a skillet over medium-low heat. Add onions and cook for about 15-20 minutes, until softened and beginning to caramelize. Add garlic, sage, and chicken sausage; continue to saute.

Meanwhile, cook pasta according to package directions. In a small food processor or blender, combine pumpkin, cottage cheese, and milk. Blend until smooth. Add to sausage mixture in the skillet and continue to cook over low heat. Season with salt and freshly ground pepper to taste.

Drain pasta and add to sausage mixture with the baby spinach. Toss together until the spinach is wilted. Raise heat if necessary to melt any remaining bits of cottage cheese, while continuing to stir until creamy. Top with Parmesan cheese, if desired.