OP - as a South Indian I can sympathize with your plight; but you are no doubt aware that fresh food is going to be very hard to come by in any airport - not impossible but hard. My suggestion is that you evaluate really how fresh the food has to be.
As an aside, asking about south indian food in NRT is equivalent to asking about sashimi in MAA. A very, very long shot. I would be doubtful even if I found something that purported to be that in NRT.
As an aside, I know the NH lounge (at least one of them) has a noodle bar. So the question is are any of the broths they use actually vegetarian, and can they whip up something vegetarian for OP? I personally really liked their offerings but then again I have no restrictions on animal products or processed foods...