Pre-heat oven to 350F.
Melt butter in a skillet.
Add squash, onion, and garlic salt.
Sauté' for 10 minutes, over medium heat, until tender.
Remove from heat; add sour cream, mayonnaise, cheddar and parmesan to the skillet; stir well.
In a small bowl, beat 2 eggs; mix well with filling.
Pour contents of skillet into a large casserole dish.
In a separate bowl, melt butter in a microwave.
Using a large baggie, crush crackers and French fried onions and mix with melted butter.
Sprinkle cracker mixture over squash casserole.
Place in pre-heated oven and bake for 30 minutes until topping is golden brown.