The best option is: buy you own food (in advance).
Airlines have different options, and non-spicy is often a default (but there are other extra options): nobody wants to give children too spicy food. And spicy in general is not so good for air travels.
Unfortunately, it seems to me that often they forget such options, or it is far worse than the normal menu (vegetarian is sometimes an exception).
I would recommend you to buy some alternative food, and then mix with what they give you (e.g. fruits and salads, etc.).
A few weeks before your travel you should check regular menus on the airline's website, you may want to change it (e.g. from/to vegetarian). Unfortunately you never see special menus, and you may change special menu only with long advance notice. [But so, be prepared with your own food. A flight delay will "erase" all your special foods].
For the other question:
Menus and codes are standardized by IATA (about what may and must not contain, not the real menu), and sent coded in the ticket information. The list is long, but usually airlines will offer only few of them (and often a very blended and reduced one, which covers many options, as a fruit salad and nothing more).