Put a large stock pot over a medium-high flame. Add the water, bouillon cubes, split peas, onion, carrots, celery and mushrooms to the pot. Bring the pot to a boil and lower the flame to a simmer. Cook until the split peas are tender and begin to break down, about 20-30 minutes.
Add the broccoli rabe and return the pot to a low boil. Cook just until the broccoli rabe is tender, about 7-10 minutes.
Portion into bowls and drizzle with good quality extra virgin olive oil. Serve with crusty Italian bread.