Rinse diced fish and slivered red onion in cold water and dry thoroughly.
In a large bowl, combine fish, red onion, lime juice, salt, habanero (if using), and ají amarillo sauce (if using). Cover and refrigerate 20 minutes.
Just before serving, stir in cilantro. Divide between 4 bowls and serve with sweet potato, corn, and lettuce leaves on the side.
Peruvian Pantry: Ají amarillo. A yellow chile with a slightly sweet flavor and plenty of heat. Available in this county in jars or as a puréed sauce at many Latin markets.
Note: Nutritional analysis is per serving.