Heat the oil in a soup pot and sauté the onions and garlic until the onions have wilted. Stir in the lentils, melon, Swiss chard, slab bacon, cumin, saffron, bay leaves, cilantro sprigs, and cinnamon. Add the water, bring to a boil, cover, and simmer 45 minutes.

Add salt, the vinegar, potatoes, and black sausage, if using. Cover and continue cooking for 45 minutes more, until the lentils and potatoes are done. If the soup is too thick, add a little water, or if too soupy, boil down. Serve in soup bowls, sprinkled with cilantro.