Preheat your oven to 350 degrees Fahrenheit. Spray a 9x13 inch baking dish with non-stick spray.
Boil the sliced squash and chopped onion in a pot. Add the water and the bacon grease.
Cook the vegetables gently until they become softened.
Drain the hot vegetables incredibly well to remove all excess water. Set them aside.
Mix the canned soup, eggs, evaporated milk, and mayonnaise in a separate bowl.
Stir the shredded cheddar cheese and seasonings into the wet mixture completely.
Add the drained squash to the wet bowl. Fold everything together gently.
Pour the entire vegetable mixture safely into your greased baking dish.
Crush the crackers into small pieces inside a bowl.
Pour the melted stick of butter over the crushed crackers. Toss to combine perfectly.
Sprinkle the buttery cracker mixture evenly over the top of the casserole.
Bake the dish for exactly 35 minutes until golden brown and bubbly.