Place the chickpeas and both beans in a large bowl, add water to cover by several inches, and refrigerate for several hours or overnight; drain.
In a large pot, combine the chickpeas and beans, add cold water to cover by 1 inch and bring to a simmer. Cook for 1 hour, adding more water if needed. Add the lentils, split peas, fennel, tomatoes, onion, olive oil, and water to cover as necessary. Cook for 1 hour more. Add the greens and salt and pepper to taste. Cook for 30 minutes, or until the soup is thick and all of the legumes are tender. (The fava beans and split peas will break apart and thicken the soup.)
Just before serving, heat the oven to 400 degrees F. Toss the bread cubes with the oil and spread them in a single layer in a roasting pan. Bake, stirring once, until toasted and crisp, about 10 minutes.
Spoon the soup into serving bowls. Sprinkle the croutons on top.
Recipe courtesy of Italian Holiday Cooking (Morrow, 2001) by Michele Scicolone