How do you cook casava?

I have been changing my diet and it's been helping me, I am losing weight and getting a lot healthier.

I stopped eating cereals, like rice and wheat, and bread.

For my carbs I eat starches, I picked up ideas from my friends of different cultures (I live in a melting pot). Carribean people when they avoid eating rice the eat plantain and sweet potato or yams, with their veggies and meats. I do the same. It's really good and digest a lot easier.

I was at a bbq 2 days ago and even tho we were a mixed group the people who's house it was, were of Sri lankan decent.

They bbq'd chicken, pork, lamb, and these fish fillets inside banana leaves (tasted so good omg) and they also bbq'd these big Casava's. It was really good filling and still not heavy at the same time and tasted really good with the meat.

I looked online about cooking casava and they said you have to be careful for if you prepare it wrong, it can be poisonous, does anybody know how to prepare casava properly?