Place the fish in a cold glass bowl (leave the bowl in the freezer a couple minutes to get cold).
Season with salt and pepper, and add the aji limo.
Add the lime juice, and let it sit for 1 minute.
Add the onion and fish broth.
Let this sit, refrigerated for up to 15 minutes before serving.
Serve on individual plates, on top of a large lettuce leaf.
Sprinkle with a little bit of finely chopped cilantro if you like for garnish, and add a wedge of boiled sweet potato and 10 gr or so of "cancha" - fried Andean popcorn which you should be able to find at your local Latin market.
If you're unable to find aji limo (a Peruvian chili pepper), you can substitute red jalapenos; and you can use key lime as a substitute for Peruvian limones.