Let users create / list their own restaurant menu I am building a site where a restaurants visitors could register. Now, I have created a content type where the restaurant owners could list up there restaurant. I have to also allow them to add there restaurant menu based on categories like 'starters', 'mains' etc.

Is there any module which could help me achieve this?
Not totally sure what you're looking for. I'm going to assume that you're looking for a particular form to create a restaurant menu from the backend.

Drupal allows you to create this functionality OOTB (out of the box):


Fields (formerly cck pre Drupal 7)
User Roles
User Permissions


You're probably going to need to output this in a pretty fashion so your best bet are some standard contrib modules:


Views
Fields Collections


Nonethless, these modules are standard fare for every Drupal project (except maybe Fields Collections).

Oh i googled and there are possibly similar questions out there on SO: 


https://stackoverflow.com/questions/5204936/restaurant-menu-drupal-7
https://stackoverflow.com/questions/4935899/best-drupal-gui-for-displaying-a-tiered-restaurant-menu
https://stackoverflow.com/questions/1835562/drupal-content-type-restaurant-design