Matoke or Matooke can be cooked in a number of ways. The Liboke (which is the proper name for the plantain and beef stew - Matoke is just the plantains) is made with all-green plantains like the ones in your picture.
When dishes call for
steamed plantains, that's usually ripe ones - and plantains have a very different ripeness scale from dessert bananas. Plantains are ripe when the skin is at least 50%
black - anything yellower/greener will still be very starchy.
EDIT - This said, whenever I've made Liboke or its South American relative, Sancocho, I've always enjoyed the results more when I used fairly ripe plantains. There's more dimension to the flavour then - and unless you know exactly how to peel a green plantain, there's less chance of getting bitter saps in the dish. Used green, they're kind of potato-ish; used ripe they're definitely more banana-y in flavour but still provide good body and filler for the stew.
If you'd like a pictorial primer on peeling green plantains in order that the bittering sap stays off the final result, I'd be happy to oblige.
Edited by Panaderia Canadiense, 28 March 2012 - 08:08 AM.