1. In a large Dutch oven, combine onion, carrots, celery, cabbage, garlic, oregano, and vegetable broth; bring to a boil, over high heat, loosely cover, reduce heat to a simmer, and let cook until tender, about 45 minutes.
2. Stir in split peas and bring back to a simmer; loosely cover, and continue to cook, stirring occasionally, until the peas are softened and starting to break down, about 1 1/2 hours.
3. Add water if soup gets too thick during the cooking.
4. Season with salt, pepper, and Worcestershire sauce; let simmer a few minutes to meld flavors, taste, and adjust seasoning and thin with water as needed.