Place the tuna, shrimp, and salmon each in a large bowl and add 1/3 of the avocado, lime juice, and cilantro to each bowl. To the tuna, add ½ of the ginger, and all of the yellow chili pepper, sesame seeds, sesame oil, and green onion tops. To the shrimp, add ½ each of the red onion, rocoto pepper, olive oil, and ginger, and all of the garlic. To the salmon, add the remaining red onion, chopped rocoto pepper, and olive oil, and all of the red bell pepper, corn, and garlic. Season each with salt and pepper to taste, and marinate for 10 minutes.
Serve the three ceviches together, each on a large decorative spoon or in a serving bowl.