Mixed Vegetable Casserole In large bowl, mix vegetables, chestnuts, cheese, celery, mayonnaise and onion. Transfer mixture to 10-inch greased baking pan or casserole pan that will fit into NuWave Oven. Place pan on 1-inch rack and cook at 350°F for 15-17 minutes. Combine crackers and butter. 2 minutes before casserole is done, sprinkle with cracker mixture. Continue to cook until brown. Let casserole sit inside dome for 1-2 minutes before removing.