Place the water into a large pot, and add 1 tablespoon salt , chopped cilantro (coriander), garlic, chicken legs, plantains, and 1 onion. Bring to a boil, and cook for about 20 minutes. Add the potatoes and cassava to the pot, and continue to cook for another 20 minutes, or until potatoes are tender.
While the chicken and vegetables are cooking, heat the oil in a large skillet over medium heat. Fry the onions in the hot oil, and season with cumin, paprika, and salt. When the onions are limp, stir in the tomatoes, and remove from heat.
Spoon the chicken stew into bowls, and serve topped with the tomato onion sauce.