Heat oil in a large soup pot over medium heat. Add onion and half the salt. Cook for about five minutes, until softened. Add carrot and celery. Cook for five to 10 minutes, until fragrant.

Add mushrooms and cook over medium heat for at least 20 minutes, preferably longer, for maximum flavor. Add remaining half of the salt and all remaining ingredients to pot.

Cover and bring to boil over high heat. Once boiling, reduce heat to a simmer and continue to cook for two to three hours, until split peas are very soft and falling apart. Remove bay leaves before serving.