Here is a collection of Cuban recipes
that will give you more than a couple to pick from.
The black bean soup from your link is neither salty (unless you add too much salt - the reason the rescipe doesn't specify an amount is because you need to "salt to taste") nor sweet- like Andy M. said ... the sugar is only used to balance
Regarding the Cuban Sandwich - here
is some history and recipes.
I've had plantains that were fried crips like potato chips (or banana chips) and I've had them cooked soft and sweet like Bananas Foster
. "Dry and Mushy" seems to be a contradition of terms - (dry being too little moisture or over cooked, and mushy too much moisture or under cooked), a bad recipe, a bad execution of the recipe, or maybe the plantains are too under ripe. Here are some plantain recipes
for you to look at.