Preheat your grill or smoker to 325°F.
Place the pre-made mashed potatoes in the bottom of your baking dish and spread evenly.
In a mixing bowl, toss the cauliflower with oil and BBQ rub until coated well.
Pour the seasoned cauliflower over the mashed potatoes layer, spread evenly, and press down into the potatoes.
Top with shredded cheese and breadcrumbs. Place the dish, uncovered, on the upper rack of your grill or smoker.
Bake for 25-30 minutes.
Remove from the grill with oven mitts or grill gloves and allow to rest for 10 minutes before serving.
