Peel squash and cut into 1/2-inch cubes. Chop onion and mince garlic.
Heat oil in a large skillet over medium heat. Once it becomes hot and begins to shimmer, add squash, onion, and garlic; season with salt and pepper. Cook for 8-10 minutes allowing onion to become translucent; stir occasionally to prevent veggies from sticking and burning.
Add broth and bring to a boil; reduce heat and simmer 15-20 minutes until squash has become soft and the broth has reduced by about half.
Meanwhile, cook pasta as directed on the package. Drain, reserving 1 cup of the liquid.
When squash has softened, remove from heat and allow to cool. Add mixture to a blender and puree.
Add back to skillet along with cooked pasta and 1/4 cup reserved liquid. Heat over medium and stir until pasta is evenly coated; add more liquid if necessary or desired. Add Parmesan and toss once more.
Serve with sliced apples on the side.