Christine,
You are asking an interesting question about one of our favorite and very versatile foods. The answer regarding whether plantains are a fruit is that yes, they are a fruit. But, they are a starchie fruit and they need cooking. Plantains are not at all like an orange or a mango that are sweet and juicy raw.
We usually eat plantains in the evening in keeping with our plan to eat light evening meals and to have fruits and grains. If we are having plantains though we won't also have grains. Plantains provide plenty of starch.
Sometimes we do eat plantains for our breakfast or lunch and then we treat them like a starchie vegetable even though technically they are a fruit.
I actually purchase five or six good sized plantains most weeks at the local Mexican market. Yumm! But, I had better explain how I cook them...
The way we cook plantains is to let them get ripe first to where the skins are starting to turn yellow. At this stage they peal easily. When they are green they are very hard to peal.
After peeling them we cut the plantain lengthwise and then cut them in 1/2 circles around 3/4 of an inch or less thick. (Sometimes I do not cut them lenghwise in which case they are circles instead of half circles after I cut them)
We then put them into a dutch oven or non-stick frying pan and toss the cut plantains with LOTS of lime or lemon juice mixing them up so that the juice is all over the plantains and there is a covering of juice barely covering the bottom of the pan.
Then we spread them across the bottom of the pan and put a lid on. My preference is a glass lid so I can see as they are cooking.
We put the heat up very high and get the lemon juice to start to simmer. Then we turn them down to a low to medium low heat and allow them to slow cook for around 20 minutes or more. The bottom of the plantains will start to carmelize which makes them SUPER delicious.
So, the bottm line is: Enjoy your plaintains. :-)
Sean