Preheat oven to 450° F.
Place 2 rimmed baking sheets to preheat in the oven. (optional, but helps cook the veggies faster and gives them a nice roasted bottom.)
Take chopped cauliflower and toss it in a large bowl with 1-2 tablespoons extra virgin olive oil. Add in nutritional yeast (if using) and salt. Toss to coat.
In another bowl, toss the tomatoes, onion, and peppers in a tablespoon of extra virgin olive oil, salt and freshly ground pepper.
Once oven is heated, take out baking sheets and line with parchment paper, if desired. Place in an even layer the cauliflower on one sheet and the rest of the veggies on the other.
Bake until nicely roasted, about 20-25 minutes.
While baking, saute garlic in extra virgin olive oil over medium heat. Add celery and cook until slightly softened.
Add in beef and brown, adding salt and pepper to taste.
Once veggies are done, remove them (except for cauliflower) from their baking sheets and add to the beef mixture. Pour in broth and vinegar and simmer until cooked down slightly. Stir in parsley.
While mixture is cooking down, place the cauliflower in a high-powered blender (I used my Vitamix) or food processor and puree. You may need to add more yeast or salt at this point.
Divide the beef mixture evenly among two 8" pie plates (or use a cast iron skillet of the same size) and top with the roasted cauliflower puree.
Bake at 375° for 15-25 minutes or until heated and the topping has a golden colour. (colour will be lighter if yeast is omitted).
Alternatively, this dish can also be prepared on the stovetop. Instead of using pie plates, use a cast iron skillet or other stovetop safe option. Cover and heat over medium until the cauliflower topping is heated through.