Place the sliced squash and onion in a saucepan.
Cover with water and add ½ teaspoon salt.
Cover the pot and cook for 10-15 minutes or until the squash and onion are tender.
Remove from heat and drain thoroughly.
Place cooked squash and onion in a large bowl.
Add in the mayo, egg, cheese, remaining salt, and pepper.
Mix to combine.
Pour into a greased 2 quart casserole dish (8x8 dish)
Top with crushed crackers.
Preheat oven to 350F.
Bake for 25-30 minutes or until bubbly and the top is golden brown.
Remove from the oven and let cool 1-2 minutes.
Garnish with chopped fresh parsley.