Yaal Restaurant is located on the marine drive in the Wellawatta Area. I have been here for take away a few times on the recommendation of a good friend. I must say food was spicy but was different to the local southern Sri Lankan food. Yaal is a name for Jaffna, which is located in the northern tip of Sri Lanka. The culture, the traditions and the food of this region is very different to that of the rest of the country, and is mainly southern indian with a local sri lankan twist. It is the food of the Northern Tamil population of Sri Lanka.
At Yaal you will find most dishes that you will get in a southern Indian restaurant, as such it is very vegetarian friendly. Word of caution look out for the spice. I would recommend the Restaurant for an authentic taste of Jaffna food.
I found the below video to be very informative, and should give you a good idea of what to expect!