I love ceviche of all kinds. It always reminds me of a most memorable trip to Peru, and Peruvians are the ceviche champions in my book. This dish has the perfect balance of tang, zing, texture, color and banging flavor. I like to drink the ceviche juice in the radicchio cup first and then bite into the radicchio with tuna, YUM.
In a medium bowl, combine all the ingredients except the avocado, radicchio, salt and black pepper. Add 1/4 teaspoon sea salt. Toss together, cover and refrigerate for 20 minutes, stirring the ceviche every 5 minutes.
Place the radicchio cups on a service platter, divide the ceviche with its the juices evenly among the cups. Top each with the avocado and season with sea salt and black pepper. Top with more cilantro, if desired.