Preheat the camp oven (closed grill or smoker) to 425 degrees F (220 degrees C).
In a skillet melt the butter over medium heat. Saute the onions and celery until the onions start to become translucent, about 5 minutes.
In the casserole dish combine the spiral pasta, onions, celery, mixed vegetables, soup, milk, cheese, and drained tuna. Mix very well ensuring you get to the bottom and into the corners. Wipe any smears from the casserole dish edges.
In order, sprinkle evenly over the top of the casserole the breadcrumbs, cheese, and herb rub.
Place the tuna casserole in the preheated camp oven. Cook for 20 minutes until the topping has melted and the casserole is bubbling. Remove, let stand for 5 minutes, and serve.