In a large Dutch oven, warm up the olive oil and cook the onion until it softens, about 5-6 minutes.
Wash the lamb, pat it dry with a paper towel and sprinkle with salt.
Add the lamb to the onions and cook until it is browned on all sides, about 10-12 minutes.
Add the wine and cook until the alcohol evaporates and the wine reduces by almost a half. Lower the heat (as low as it will go), cover and cook for about an hour. The lamb should fall apart when pierced with a fork. If you are using regular lamb (not young), cook the lamb for at least 2 hours over very low heat.
When the lamb is almost done, add the peas and cook for about 5 minutes for the peas to cook and the flavours to blend.
Season with salt and pepper to taste.
Sprinkle with the grated pecorino and serve hot.