1. Meat Loaf. Heat oven to 350 degrees F. Combine ground beef, sweet potato, zucchini and onion in a medium bowl. In a small bowl, whisk egg, bread crumbs and milk. Add to bowl with meat mixture along with Italian seasoning, salt and pepper. Gently mix together. Shape into a loaf, about 7 inches long by 4 inches wide on a rimmed baking pan. Spread ketchup on top.
2. Bake at 350 degrees F for 45 minutes. Let rest 10 minutes before slicing.
3. Meanwhile, prepare Cauliflower. Bring a large pot of water to boiling. Add cauliflower and cook 10 minutes. Drain well and return to pot.
4. Melt butter over medium heat in a small saucepan. Whisk in flour and cook 1 minute. Whisk in milk and bring to a simmer. Cook, stirring, 1 minute.
5. Combine sauce, salt and cayenne with cauliflower. Mash or puree with a blender or immersion blender.