Soak fish in lemon juice making sure the fish is fully submerged in the juice. Let fish cook in juice for 25 minutes, but not longer than 30 minutes. Strain out the lemon juice, reserve for later use.
While the fish is marinating, prepare the remaining ingredients. Start with the cucumber, tomato and green onion. Drain the lemon juice out of the fish but save it because you’ll be adding some back into the ceviche.
Finally, chop the cilantro, dice the avocado and add them to the ceviche. Pour about 1/4 cup of the reserved lemon juice over the avocado and mix everything well. Serve with tortilla chips.
When you choose a serving dish, make sure you use one that will allow the fish to be fully submerged in the lemon juice and support all the ingredients later.
Cover it with plastic wrap or a lid if you’re baking dish has one, and keep it in the coldest part of your fridge for 25 minutes.
If you’re serving ceviche at a party, don’t bring it out until guests start arriving. When it’s time to bring it out, keep a layer of ice under the dish that it’s in and keep it covered. If you’re making this for lunch for your family, there’s no need to keep it on ice as long as it’s all being eaten in that one sitting.