Prepare Sweet Potatoes: Peel and cut sweet potatoes into medium sized chunks. In a large saucepan, combine the potato chunks with salt and the cracked cardamom pods. Cover with cold water, bring to a boil, then reduce the heat, cover, and cook for about 30 minutes until tender.

Make Filling: Chop garlic, ginger, and onion, then blend with cardamom, cumin, and coriander until finely chopped. Heat coconut oil in a heavy pan and add the paste. Cook for a few minutes, stirring then stir in garam masala, chili flakes, turmeric, and lamb mince, breaking it up.

Add Liquids: Add chopped tomatoes and using the empty tin fill with water and pour this in. Stir in red lentils, season with salt and Worcestershire sauce. Bring to a simmer, cover, and cook for 25 minutes, stirring occasionally.

Prepare Mash: Once the sweet potatoes are cooked, drain and let cool slightly; mash them in a bowl, adding some cooking water for a spreadable consistency. Squeeze in the juice of half a lime to taste.

Assemble: Divide the lamb filling among 4 small ovenproof bowls or one large dish. Top with the sweet potato mash, spreading it evenly.

Bake: Place the dishes on a tray and bake for 10-15 minutes (or 30-35 minutes for a large dish) until hot and bubbling.

Serve: Sprinkle with pistachios before serving. Enjoy your delicious shepherd's pie!