In a large mixing bowl, combine the fish with the onion, lime juice, and chile; season with salt and pepper. Toss gently to combine, being sure to coat the fish with the lime juice. Cover and refrigerate for 30 to 45 minutes, do not marinate longer or the acids from the lime will make the fish mushy. Serve cold with cilantro and canchita on top. .
Heat the oil in a large pot over medium-high heat for 2 minutes. Add the chulpe corn, cover the pot and reduce the heat to medium. Once you hear the kernels pop (like popcorn), shake the pot vigorously to prevent the kernels on the bottom from burning. Once the popping slows, after about 6 to 8 minutes, drain the canchita on a platter lined with paper towels to remove excess oil. Season with salt while the corn is still warm and serve with ceviche.
The aji amarillo is traditional chile in Peru and available at any Latin grocery but not in many mainstream supermarkets. In substitute you can use a habanero or any other hot chile.