Put the green split peas into a fairly large pan, with around 1.5 litres of water. Bring to the boil and let simmer for around 40 minutes. You need to keep a close eye, as the water can boil off pretty quickly. You may need to top up the water levels.
Drain the green split peas, then pop them back into the pan, add all the other ingredients and adding 1.5 litres of water again. Mix well, and bring to the boil, letting this simmer until the water reduces by about two thirds. Be careful you don't leave this alone as it will burn quickly if you do. I added a good measure of salt and pepper at this stage. Some people add basil and thyme, and even rosemary, but I know my boys wouldn't eat that, so I leave it out.
Add your slushy peas mix to a baking tray, and let it set in the oven for around 25 minutes, at 180 degrees C. Your oven might take slightly less time, or more. It won't set firmly at all, but will be easy to cut when it's ready.
I cook my meat separately, and add it to the top of the peas pudding in the last five minutes, before removing from the oven. Some people add it when it first goes into the oven, and cook it as part of the dish.