In a large pot, heat the vegetable oil over medium heat. Add the onion and scallions and sautué until onions are translucent, about 3 minutes. Then add the tomatoes, garlic, salt and ground pepper and sautué for 5 more minutes.
Add water, yuca and cumin powder. Reduce the heat to medium low, cover, and cook for 10 minutes, stirring occasionally.
Add Fish steaks and cilantro and cook for an additional 15 minutes or until the fish is cooked and the yuca is tender.
Serve with white rice and fried sweet plantains on the side.