Preheat oven to 400 degrees F. Spray a large sheet pan with oil.
In a large bowl, add the squash, onion, oil, salt and pepper, to taste. Toss to evenly coat.
Spread in an even layer on prepared sheet pan. Roast for 20 minutes.
Remove sheet pan from the oven and add the bacon and 2 tablespoons of the Parmesan. With a spatula, toss the veggies and mix in the bacon and Parmesan.
Put sheet pan back in the oven and cook an additional 20 minutes.
Sprinkle with remaining Parmesan and garnish with parsley.