Preheat your grill to around 350 to 375°F, lighting all burners and keeping them on low. Also, preheat your side burner to medium.
Using the side burner and a dutch oven with lid, melt 3 tbsp. of butter and add the onion. Cook the onion, stirring periodically, until it becomes a golden color, being careful not to burn it.
While the onion is cooking, bring a pot of water to boil and cook the potato slices for 10 minutes, or until they’re half way cooked. Drain and remove them from heat.
Once the onion is a beautiful golden color, move the onion to the side of the dutch oven and add the remaining butter. Add the chilies, ginger, garlic, and spices. Fry them in the butter for a moment until fragrant, then mix them with the onion. Add the lamb, lentils, and tomatoes. Bring everything to a simmer, then place the lid on the dutch oven, and place onto the grill over direct heat for 20 to 30 minutes, or until your keema has become a thick stew. Stir every 10 minutes or so, to make sure that everything is progressing nicely. You may need to mash the lentils a little.
Once you have moved the dutch oven onto the grill, you can work on the potatoes. Melt the butter, and whisk in the curry powder. Coat the potatoes with the melted butter, adding salt and pepper to taste. Grill the potatoes over direct, low heat, until they are crispy with lovely grill marks on both sides, and are fork tender – a fork will pierce the potato easily and then it will slide right off the fork.
Serve the keema and potatoes together, topped with a dollop of fresh plain yogurt and sprinkled with fresh cilantro.