With lots of veggie shortcuts and a cauliflower-mash topping instead of spuds, you can have this comfort-food staple in a fraction of the usual time—and save carbs too! Cook the veggies from frozen; no need to thaw. Swap ground turkey for the beef if you prefer.
If you don't have an ovenproof skillet, you can transfer the beef mixture to a medium baking dish or 4 individual baking dishes after removing it from the heat in Step 3. Continue with Step 4 as written (divide the cauliflower mixture and cheese among the baking dishes if using individual-size dishes).