Add oil and onions to a dutch oven or heavy pot over medium heat.
Saute the onions for 15 minutes, or until they turn golden brown. Then, add the garlic, ginger and serrano pepper. Stir-fry for a minute.
Add the spices, stir-fry, then add the tomatoes. Mix well and cover the pot for 5 minutes.
While that's cooking - combine the coconut milk and fresh mint in a blender - and blend. Set the sauce aside for now.
Add the ground lamb to the pan and once it’s completely browned and cooked through, add the mint sauce you just made.
Cook for another 5 or so minutes, garnish with more mint and serve.