A recipe for the same (also variantly known as pease porridge or pease pottage, depending on where you come from) follows. It's my Nana's recipe with the addition of a little garlic, since she was of a generation that didn't hold with 'foreign stuff' (except when it suited them, of course).
500g dried green peas
1 small onion, shredded
1 clove garlic, finely chopped
1 tsp dried sage
Pick over the dried peas to remove any grit, discoloured ones and so on. Rinse. Place in a large pan and cover with cold water. Bring slowly to the boil, and simmer, replenishing the water as necessary, until the peas are tender.
Add the onion, garlic and sage. Stir well, and return to simmering until the onion is cooked. Season with pepper and salt.