Preheat oven to 350°F. Grease an 8x8 baking dish.
In a large bowl, mix together the celery, onion, bell pepper, cheese, corn, green beans, soup and sour cream until fully combined. Season with salt and pepper as needed.
Transfer the veggie mixture to the prepared baking dish and spread into an even layer.
Top the casserole evenly with the crushed crackers. Drizzle the melted butter over top.
Bake for 40-45 minutes until hot, bubbly and lightly browned on top.
Let stand 5 minutes before serving hot.