It's traditionally made with pearl barley, but you can use split peas or both instead.
Softena chopped onion, chopped celery and carrot in some butter or oil.
Add some veg stock or water with shredded leftover lamb.
You can also add other veg - cubed potatoes, turnip or swede.
Season, bring to the boil and lower the heat to a simmer.
Add you pearl barley and / or split peas and simmer until cooked through.
Serve with a good scattering of fresh parsley.