Preheat the oven to 350 degrees F.
Lightly oil a 9 inch bake dish, then set to the side.
Melt the butter in a large pan over medium heat.
Once the butter is melted add in the squash & onions.
Saute' until translucent, then toss into a large mixing bowl.
Add in the cheddar cheese, parmesan, and sour cream.
Mix until well combined, then sprinkle in the salt & peppers.
Fold the ingredients, then add the mixture into the 9 inch bake dish.
Sprinkle the crushed fried onions on top.
Bake, uncovered, for 20 minutes or until golden.
Remove from the oven, and let cool.
Serve & enjoy!