Hi Fi5H
It's a strange one this. A quick search on google throws up nothing more than, a few famous people in various fields with the name Roshan Lal? I'm sure that you have already done this?
From your description of the dish, It does like, what is described on many menus in Manchester as a Rogan Josh. I'm wondering if it is perhaps a corruption of the words Rogan Josh, a bit like Matsaman is a corruption of the word, Muslim? However, if you also have Rogan Josh on the same menu, then bang goes that theory.
Sorry not to be of more help

Ray
