Preheat oven to 350 degrees and grease a 13×9 baking dish. In a bowl, mix white cake mix, vegetable oil, water, and eggs together. Once combined, add in pumpkin puree, brown sugar, pumpkin pie spice, cinnamon, allspice and vanilla extract.
Peel cucumbers and cut in half. Spoon out the seeds and cut the cucumbers into small chucks. With a beater, mix cream cheese, mayo, milk, salt/pepper, and garlic powder. Add cucumbers and green onions. Mix well. Best if served with Cool Ranch Doritos.
Combine eggs with milk. Add remaining ingredients except cereal and butter. Pour into a 10x6x2-inch baking dish. Combine slightly crushed cereal and butter. Sprinkle over top. Bake at 350 degrees for about 50 minutes.