In a Dutch oven heat 3 tablespoons olive oil over medium-high heat until hot but not smoking. Add onion and saute until just beginning to soften, about 5 minutes. Add pancetta and peas and toss. Add the ground lamb, season with salt and pepper and cook 8 to 10 minutes. Let cool, add eggs and chili flakes and stir through fat, about 3 to 5 minutes. Remove from the heat and let cool. Once the meat mixture is cool, add the bread crumbs, grated cheese, and parsley, Stir to blend.
Use the mixture to stuff the leg of lamb, dividing the stuffing evenly throughout the meat flaps created by the butterfly cut. Use butcher's twine to tie the leg so that none of the stuffing will spill out. Season with salt and pepper.
Heat the remaining 3 tablespoons olive oil in the 12-inch saute pan over high heat. When the oil is hot but not smoking add the stuffed leg to the pan and sear it. Pour in the white wine and allow it to evaporate. Season, to taste, with salt and pepper and cover with the lid. Lower the heat to medium and allow the leg of lamb to cook until medium, about 45 minutes. Add water when necessary to keep the leg from sticking to the pan. Serve hot, drizzled with gravy from the pan.
Recipe courtesy of Mario Batali