Preheat the oven to 350F. Spray a 9x13 pan with nonstick spray.
In a large bowl, combine the mixed vegetables, potatoes, onion, mayo, seasoning, celery soup, and cheese.
Spread into the prepared baking dish.
Melt the butter in a small bowl. Crush the crackers and mix with the melted butter.
Top the mixture with the butter/cracker crumb mixture.
Cover and bake for 20 minutes.
Uncover and bake for another 10 minutes or until bubbly and the crackers are golden brown.
Remove and serve.