If the planet is owned by a player, it will always start with a frigate factory, but you can add more. 

Right click on the planet you wish to edit, and choose the "edit" option.  This will open a window for you.  Under "group manager" click the "add" action.  This will allow you to use the group editor.

You can now click on individual items (such as gauss cannons) to have them spawn into the planet, and also change the conditions on which they spawn.  You should probably ensure that TEC gauss cannons spawn only for a TEC player, and the other races get their own equivalent.  Just as an aside "cannon" means superweapon, so be mindful that if you place two or three "cannons" in your worlds they start with two or three superweapons.