Preheat the oven to 400°F and grease a spacious baking dish with your preferred cooking fat. In a skillet, cook the bacon over medium heat until crisp, then chop it into small pieces and reserve. Steam the cauliflower florets until tender enough to pierce with a fork. Transfer them to a high-powered blender and process until they form a cohesive blend. Incorporate the nutritional yeast, garlic powder, onion powder, white pepper, salt, and eggs, then blend until the mixture becomes completely smooth and creamy; set aside.

Meanwhile, in a large sauté pan, cook the ground beef with the chopped onion and minced garlic, breaking it into small bits as it browns. Lightly season with salt during the browning process. Once cooked through, stir in the ketchup, mustard, and mayonnaise. Mix well, then season again with salt and pepper to your preference. Fold in half of the reserved bacon.

Distribute the beef mixture evenly in the prepared baking dish. Carefully spread the cauliflower purée on top, smoothing it out into a uniform layer. Scatter the remaining bacon over the surface and add a light sprinkle of freshly ground black pepper.

Bake uncovered for 20–25 minutes, or until the top layer develops a slight golden hue. Garnish with freshly chopped green onions just before serving.