Step 1Heat the oil over medium-low heat in a large, heavy soup pot or Dutch oven and add the onions. Cook, stirring, until they begin to soften, and add the leeks. Cook, stirring, until the vegetables are tender and translucent but not browned, about 5 minutes. Add the carrots and celery and a generous pinch of salt, and continue to cook, stirring often, until the vegetables are tender and fragrant, 5 to 10 minutes. Stir in the cabbage and the garlic, add a little more salt, and cook until the cabbage has wilted, about 5 minutes.
Step 2Add the water, potatoes, turnips, canned tomatoes with liquid, half the green beans and oregano and bring to a boil. Tie the Parmesan rind, bay leaf, thyme and parsley sprigs together with kitchen string, or tie in cheesecloth, and add to the pot. Add salt to taste (at least 2 teaspoons), reduce the heat to low, cover and simmer 45 minutes.
Step 3While the soup is simmering, blanch the remaining green vegetables: Bring a pot of water to a boil, drop in the shelled favas and boil 1 minute. Remove from the water using a slotted spoon or skimmer and transfer to a bowl of cold water. Drain and pop the skins off the favas. Set aside. Bring the water in the pot back to a boil, add a teaspoon of salt and the peas and remaining green beans. Boil until just tender but still bright green, 5 minutes. Remove from the water using a slotted spoon, refresh with cold water and set aside. Retain the cooking water in case you want to thin out the soup later.
Step 4Stir the canned beans into the soup, then add the greens and the pasta and simmer until the pasta is cooked al dente, 10 minutes. Stir the cooked peas, favas and green beans into the soup. Grind in some pepper and taste. Does the soup taste vivid? Does it need more salt? (Probably). Or garlic? It should be savory and rich-tasting. Adjust seasonings as necessary. If it seems too thick, thin out with a little cooking water from the green vegetables.
Step 5Remove the Parmesan rind bundle, stir in the chopped parsley, and remove from the heat. Serve in wide soup bowls, with a tablespoon of Parmesan sprinkled over the top.