Wrap the naan in foil and warm in a 250 degrees oven. In a large skillet, melt the butter over medium-high heat. Add the onion and cook, stirring occasionally, until soft and lightly browned, about 7 minutes. Add the scallion whites, curry paste and ginger and cook, stirring, for 30 seconds.
Crumble the lamb into the pan, season with salt and pepper and mix well. Cook, stirring occasionally, until the meat is just cooked through, about 3 minutes. Stir in the yogurt and peas and gently simmer until warmed through, about 5 minutes. Stir in half of the scallion greens. Top with the remaining scallion greens and serve with the warm naan.