Can you TWF with just unarmed?

[Lord Vukodlak]

When the book says their is no off hand for a monk they simply mean when you flurry it can be with any part of our body its just part of the normal attack routine. More fluff then anything.

But down to the rules, yes you can, the off hand attacks follow all the normal rules. But you could have main hand +15/+10/+5 and off hand +15/+10/+5
[not accounting for any bonuses or penalties on attack rolls for simplicity].
You can even flurry at the same time gaining two additional attacks on your main hand.

The quickest way to look at it is this,
A monk can do TWF with his unarmed strike and a manufactured weapon, simply remove the manufactured and replace with a fist.