Bring a large pot of salted water to a boil. Add cauliflower florets and steam or boil until fork-tender, about 10–12 minutes. Drain thoroughly, then transfer to a clean kitchen towel or paper towels. Press firmly to remove as much water as possible.

Place plain pork rinds in a food processor or blender. Pulse until they form a fine, flour-like consistency. Measure out ½ cup and set aside.

Heat 1 tablespoon avocado oil in a large, oven-safe skillet over medium-high heat. Add half the ground lamb and cook until deeply browned, about 5–7 minutes. Transfer to a plate with a slotted spoon. Repeat with remaining oil and meat.

Reduce heat to medium. Add onion, celery, and mushrooms to the skillet. Sauté 6–8 minutes until softened and mushrooms have browned. Add garlic and tomato paste, stirring constantly for 1 minute.

Return browned meat to the skillet. Add broth, tamari, thyme, and rosemary. Bring to a simmer, scraping up browned bits. Reduce heat and simmer uncovered 15–20 minutes until liquid reduces. Stir in peas and carrots during last 5 minutes if using. Season with salt and pepper. If using xanthan gum, sprinkle over filling and stir well.

Preheat oven to 375°F (190°C). In a large bowl, mash pressed cauliflower until smooth but not puréed. Add softened butter, pork panko, Parmesan, beaten egg, garlic powder, salt, and nutmeg. Stir until fully combined and thick.

Spread filling evenly in skillet (or transfer to a 9×13-inch baking dish). Spoon topping over filling and spread to edges. Use a fork to create decorative swirls. Place on a baking sheet. Bake for 20 minutes, then broil for 2–4 minutes until topping is golden brown and slightly puffed.

Let the pie rest for 10 minutes before serving. Garnish with fresh parsley or thyme if desired.