Cook squash and onion together in boiling water until soft (not squishy), drain in colander.
In a large bowl, combine squash and onion with the next 7 ingredients and stir to combine.
Salt and pepper to taste.
Pour into a large greased casserole dish.
In a large ziplock bag, crush the saltine crackers, add bread crumbs and parsley.
Pour melted butter over the mixture in the bag and mix it together to coat all the crumbs with butter.
Pour the cracker/crumb mixture on top of the casserole.
Bake in a 350 degree oven until bubbly and top is golden brown. About 30 minutes.
Notes
I used yellow squash and zucchini in this pictured version. I was a tad short of yellow squash. This is not a deviation from the Southern-ness of the dish, as many recipes call for both.