For the Flavorful Filling:
Warm the olive oil in a large saucepan over medium heat. Add the diced onion and minced garlic, cooking until they're soft and clear.
Stir in the ground beef (or lamb), breaking it apart as it browns. Cook until it's completely done.
Mix in the diced zucchini and crushed tomatoes. Give it a good stir.
Lower the heat to a gentle simmer and let it cook uncovered for about 10 minutes, allowing the flavors to meld beautifully.
For the Creamy Cauliflower Topping:
Bring a large pot of water to a boil. Add the cauliflower florets and boil until they are very tender, about 8-10 minutes.
Carefully drain the cauliflower, making sure all the steam escapes. This helps create a wonderfully dry and creamy mash.
Transfer the hot cauliflower to a food processor. Add the butter, heavy cream, shredded cheese, salt, and pepper. Process until it's perfectly smooth and creamy.
To Assemble & Bake:
Spread the savory ground beef mixture evenly at the bottom of a large casserole dish.
Gently spoon the creamy mashed cauliflower on top, covering the meat layer completely.
Bake in a preheated oven at 350°F (175°C) for 20-25 minutes, or until the filling is bubbling and the cauliflower topping is lightly golden brown.