Heat the olive oil in a large skillet over medium heat, and sauté the onion and garlic until tender. Add the carrot and zucchini, and cook until they start to soften. Add the ground beef, salt, and chili powder, and cook until the beef browns and all of the moisture begins to dry out.
Meanwhile prepare the mashed cauliflower. Chop the cauliflower heads into small chunks, and steam until they soften (a fork can easily pierce). Add the steamed cauliflower, roasted garlic and salt to a blender and blend until you have a smooth puree. Use the tamper to help blend the cauliflower if you have one.
To assemble the pie, distribute the ground beef evenly in the bottom of an 8-inch baking dish. Spread the mashed cauliflower over the top of the ground beef, and bake in a preheated oven to 350°F for 25 minutes. If you're adding cheese (I use mozzarella) to the top of your Shepherd's Pie like I show in the video, sprinkle the cheese on top after you bake it, and then broil it until the cheese browns (about 3 more minutes in the oven).
*Roasted Garlic - Using a sharp knife, cut 1/4 inch from the top of cloves, exposing the individual cloves of garlic. Drizzle with olive oil, and bake in a preheated oven to 400°F for 25 to 30 minutes, or until the cloves feel soft when pressed. Watch the video above to see how I do it.Tip: In the video above you see me adding cheese and egg on top of my Shepherd's Pie. Both these ingredients are optional. If you are not adding cheese to your pie, and you want it to brown during baking, brush an egg over the top of the mashed cauliflower before you bake it. The nutritional values you see above were calculated without adding cheese or egg.Use all organic ingredients if you can. For the ground beef, be sure it is grass-fed, and for the salt I prefer using finely ground pink Himalayan salt.