Rinse diced fish. Place diced red onion in cold water.
In a large bowl, combine key lime juice, salt and pepper, Peruvian aji amarillo, garlic, celery, ginger, and cilantro. Add the fish and the onion.
On a plate place a piece of sweet potatoes and corn on a side, place the ceviche in the middle. Garnish with a sprig of cilantro