1. In a medium pot, sauté onions in oil. Add the split peas, ham bone, and enough water to cover ingredients; season with salt and pepper.
2. Cover and cook until there are no solid peas left, just a green liquid, about 2 hours. Stir periodically while cooking, adding more water as needed to keep the ham bone covered.
3. Once the soup is a green liquid, remove from heat. Remove the ham bone and pull or cut off any remaining ham pieces; discard the bone and return the ham to the soup and let stand so it will thicken. Once thickened, you may need to heat through to serve.