Preheat your oven to 350°F. Grease a casserole dish with spray and cook and set it aside.

In a large pan melt half the butter and fry the onion and the squash with the thyme and a pinch of salt and pepper. Sautee for 2-3 minutes stirring. Take it off the heat and allow it to cool.

Add half the grated cheddar cheese, sour cream, mayonnaise, eggs, and a pinch of salt and pepper to a large bowl, and whisk well to combine.

Mix the cooked zucchini and onion into the sour cream mixture until it is coated all over.

Pour the whole mixture into the greased casserole dish.

Crush the crackers until they form a course crumb then mix it with the melted butter and the Parmesan.

Pop the casserole into the oven and bake for 20 - 25 minutes until set and golden brown.