Preheat the oven to 350 degrees F
Add the oil in a large skillet set to medium heat. Add the squash and butter. Cook until soft about 7-8 minutes
Pour the squash into a large bowl. Stir in the Parmesan cheese, 1 cup of the cheddar cheese, sour cream, Italian seasoning. Add garlic salt and pepper to taste.
Pour into a 9x13 greased baking pan. Sprinkle the remaining 1/2 c of cheddar cheese on top. Set aside.
Add the crushed crackers into a gallon Ziploc bag add the melted butter. Toss to coat the crackers. Spread evenly over the top of the casserole.
Bake for 20 minutes or until golden and bubbly.