Preheat the oven to 425° F. Lightly spray a baking sheet with oil. Cut the sweet potato into 1/2-inch cubes. Sprinkle the sweet potato with salt and pepper. Roast the sweet potato for 20 - 30 minutes, flipping it every 10 minutes. You want the sweet potato crisp and golden brown with some black edges. Set aside.
Bring a pot of water to a boil. Sprinkle salt in the water. Add the ear of corn and boil for 5 minutes. Remove the ear of corn and cool completely. When the ear of corn is cool, remove corn kernels while still intact by slicing your knife downward as close to the base of the kernels as possible. Repeat until all the kernels have been removed.
Cut the fish into 1/2-inch cubes. Place fish in a bowl and season with salt. Set aside in the fridge.
Thinly slice 1/2 a red onion and place it in a bowl of cold water with ice. Soaking the red onion in cold water with ice helps get the "bite" out of the onions and makes them sweeter. It also helps keep the red onions crisp. Set aside.
Now we will prepare the Tiger's Milk. Only make this when you are ready to marinate the fish - the citrus needs to be fresh! Add the fresh lime juice, clam juice, 1/4 cup diced red onion, fresh ginger, and garlic clove into a blender. Pulse for 15 - 30 seconds or until smooth. Add the Aji Amarillo paste and cilantro and pulse again for 5 seconds. Strain the Tiger's Milk into a container.
Pour the Tiger's Milk over the fish and gently toss the fish to get fully marinated. Let the fish "cook" for 30 minutes or until the fish turns white. The fish ceviche should look like medium-rare steak. Cooked on the outside (opaque) while slightly raw on the inside.
Add the fish, sliced red onion, sweet potato, corn, and fresh cilantro to a bowl. Pour some Tiger's Milk over the ceviche and serve immediately.