In a large pot, heat the oil over medium high heat; saute' onions until tender and beginning to brown, 8 to 10 minutes. Grated the carrot into the pot, using the course side of your grater. Add the celery, saute' for 3-4 minutes more. Add the barley, split peas,dried mushrooms,broth and water. Bring to a boil, then partially cover the pot and decrease heat to low, so the soup simmers gently. Cook for about 1½ hours, until the lima beans and barley are tender and the split peas have dissolved. After about 45 minutes into this time period add the salt and pepper. At the end of cooking add a little more water or broth if necessary, to bring the soup to the thickness you like. Add salt and pepper to your liking.