Preheat the oven to 400F and roast whole head of garlic for 30 minutes (add in mashed potatoes).
Cook the potatoes in a large pot until tender. Then drain, mash, and stir in the remaining mashed potato ingredients until combined. Set aside for later.
Meanwhile, in a large sauté pan, cook the ground beef until browned, crumbling it with a wooden spoon as it cooks.
Cook the onion and mixed veggies into the ground beef. Stir in the flour to help thicken the sauce. Add the tomato paste, and scrape the bottom of the pan with your wooden spoon to loosen any of those tasty brown bits.
Add the remaining ingredients. Season the sauce with jerk season garlic, onion powder , cumin, chipolte lime, thyme and rosemary. Give everything a good stir, and cook the mixture until it reaches a simmer. Reduce the heat to let it simmer for a few more minutes, so that those herbs/seasoning can really season the sauce. Season with salt and pepper to taste.
Start layering the dish by transfering the filling mixture to a 9 x 13-inch baking dish, and spread it out in an even layer. Spoon the mashed potatoes on top and carefully spread them out in an even layer as well ending topping it off with mexican cheese mix..
Put the casserole in the oven for about 20 minutes, or until the potatoes or cheese if using, are lightly golden and the filling starts to bubble up around the edges. If you would like the potatoes to be a bit more browned, you can turn on the broiler for 1 or 2 extra minutes.
Garnish and serve. Remove the pan from the oven, sprinkle with a few extra herbs. Serve while warm and enjoy!