This is my twist on the traditional Mexican ceviche (which differs from that of South American cuisine). It's a very colorful and appealing appetizer dish, and is exceptionally low in calories. The shrimp is "cooked" chemically by the acid in the lime juice, rather than physically (with heat). You may substitute a good-quality white fish, such as halibut or mahi-mahi, for the shrimp, if desired. Depending on how fast and skilled you are with your knives, and whether you use fresh-squeezed or bottled lime juice, the initial prep for this ceviche can take anywhere from 15 to 60 minutes.