Promised I'd post how I make green plantain porridge. You can also make this with green bananas. They both need to be actually unripe.
Peel the plantains. I generally cut the tops and bottoms off, then score a couple of lengthwise slits in the skin and manually peel them away from the flesh. That doesn't always work with really green fruit. Push come to shove, you can just slice the skins off, sort of like you would with a potato.
Once you've peeled them, grate them. I use the fine side of the grater.
Put the grated plantain in a saucepan. Cover with water. Bring to a boil, then turn it down and simmer, stirring occasionally, until the plantain is cooked. It should be soft, about the texture of a boiled potato.
Add milk. I use a non-dairy milk, such as almond or coconut.
Add a pinch of salt and fresh-grated nutmeg and/or ginger to taste.
Simmer, stirring often, until it has a consistency similar to oatmeal porridge. This part shouldn't take too long.
To serve, I usually add brown sugar or some other sweetener, vanilla, and a dab of butter.