My son-in-law makes this wonderful ceviche for us every Christmas and New Years, and for the 4th of July too! Everyone loves it! Serve the ceviche well-chilled in small plastic cups or chilled cocktail glasses (I suggest placing the bowl of ceviche within a larger bowl full of ice to keep it icy cold), along with tostadas chips or tortilla scoops and some chili sauce on the side. Very delicious and refreshing! Note: amounts are approximate-- feel free to adjust measurements to suit your own tastes. Cook time is chill time.
In a medium bowl, mix together the chunks of shrimp (and crab if using) and the juice of one lemon; season to taste with salt and black pepper. Set aside and chill (in the refrigerator or on ice) for 30 minutes to 1 hour.
Meanwhile, prepare the ceviche by combining all the ingredients (add the avocados last, just before serving) in a large bowl with ice water, stirring well to combine. Drain well; fold in the shrimp, and season to taste with garlic powder and lemon pepper.
Keep well chilled (preferably on ice) until serving time.
Serve with tortilla chips and optional chili sauce.
Ceviche must be served well-chilled, and is best served on the same day it is made.