This dish is considered Ecuadorian comfort food and is often served for breakfast. Its foundation is a thick mixture achieved by partially blending cooked yuca pieces and vegetables from the broth.
The most important component is the pickled onion mixture (curtido) added to the soup just before serving.
Rinse the thinly sliced red onion with cold water to remove its harsh bite. Drain well.
In a small bowl, mix the onion with the lime juice and salt. Add tomato slices if using.
Let it marinate for at least 30 minutes, ideally 1 hour. The onion will turn a pinkish color.
In a large pot, combine 2 liters of water, yellow onion, green bell pepper, tomato pieces, garlic, cumin, achiote, and salt. Bring to a boil and simmer for 15 minutes to release the flavors.
Add the whole pieces of tuna (or other fish) and the cilantro bundle. Cover and cook for about 10–15 minutes, until the fish is cooked through.
Carefully remove the fish, let it cool, and then shred it into large chunks. Set aside.
Add the peeled yuca chunks to the boiling broth. Cook until the yuca is tender but still holds its shape (about 20–30 minutes, depending on freshness).
Once cooked, remove the yuca from the broth. Find and remove the stringy core located in the center of each piece.
Blend about half of the cooked yuca and half of the cooked vegetables from the broth using an immersion or standard blender with a cup of the broth to create a thick paste. Return this mixture to the pot with the broth to thicken the soup.
Return the remaining yuca (cut into bite-sized pieces) and the shredded fish to the thickened soup.
Bring it to a light simmer and season with salt and black pepper. Ideally, add a final squeeze of lime juice at the end.
Serve hot in bowls. Each serving should contain chunks of yuca, shredded fish, and the thick soup.
Generously crown the soup with the prepared pickled onion (curtido) and sprinkle with fresh cilantro.
Serve with lime wedges for seasoning, chili sauce, and crispy sides like Chifles (plantain chips) or toasted corn.