First things first, let's look at making the crust. Although your calzone ends up looking kind of like a pie, the dough is much more bread-like.
1 kilo flour
1 tbsp. sugar
1 tbsp. salt
1 cube of active yeast
You can mix the dough either on a tabletop, or in a large bowl. Create a small indentation in the middle of the flour and pour in a bit of warm water, then crumble in the yeast. When the yeast has dissolved add the sugar and salt and mix until they dissolve, too. Gradually mix in the flour, adding water as needed to achieve the consistency of dough. It shouldn't stick to your hands, nor should it be so dry that it crumbles. Knead the dough for at least 8 minutes, adding either flour or water, as necessary. Lightly flour the surface of your dough and cut a cross into it. This has religious connotations, "blessed bread" and all, if you prefer an "x" will do the trick just as well, but the cut also serves to allow the dough to rise. At this point, it should look something like the photo below...
Wrap this baby up in a dry cloth, then stick it under the covers in your bed...or in some other warm spot...and let it rise for about an hour and a half. On to the filling:
pitted black olives
grated pecorino or romano cheese
I know you are going to be thinking...how much of each of these ingredients? And I can only tell you that...it depends! It depends on how you like your calzone. Like so many recipes passed on through the oral tradition, you just have to try and see how it comes out, then make adjustments to suit your taste the next time. In any case, the onions are the key ingredient here, so you probably want about a kilo of them.
Boil the cod until they are firm and white inside. Clean them, discarding all the skin, bones, etc. and set the meat aside.