Though it may look little traditional and many of you may not have heard of this. Yes there exists a variety of fast food (though placing these in that category with current wrong meaning may be injustice to that) is South Indian breakfast items like Idli, Dosa, Utpam, Upma etc.
I do not have enough resources to turn this into a big international chain like McDonalds or Burger King but it can turn into so.
For starters Idli is a steamed rice/pulse dumplings, Dosa is again fermented grinded rice/pulse hot pan cake (not exactly like that).
This is very healthy, light but still can be eaten on go and atleast Idli can be prepared very fast if initial preparation is already done.
And top of it all these are vegetarian and very tasty.