Bring salted water to a boil in a large pot set to high heat.
Fill a large bowl with ice and water.
Drop cauliflower into the boiling water and cook for 2 - 4 minutes. (see note)
Drain cauliflower and place in the bowl with ice water. Let cool.
Chop cauliflower into small pieces.
In a large bowl combine the cauliflower, tomato, cucumber, onion, chile, cilantro, and lime juice and mix well.
Season with salt and pepper, and let marinate for 30 min.
Adjust seasoning and serve on top of avocado halves with chips or tostadas.
Video
Notes
Let your ceviche marinate for at least 30 minutes to let the flavor develop. If possible a couple of hours before would be best.
Add 1 tbsp. of nori or dulse flakes to give this ceviche a fishy flavor.
Cook the cauliflower according to your preference. Cooking it for 2 minutes still leaves it crunchy. When you cook it for 4-5 minutes then the cauliflower is tender.