Saute the zuchinni and onions in the butter until tender, pull pan off and allow it to cool slightly so that you can add the eggs and milk without cooking the eggs.
Once your pan is slightly cool you can add your eggs and milk, stir, add your salt and pepper, and then put the veggie mixture into a greased casserole pan with lid, top with cheese and then your crackers. Note: my hubby added some french onions to the top as he is addicted to them! That is an option but not required.
Bake at 350° for 35 minutes or until cheese is melted and top is slightly brown.