At certain Cargills Food City outlets you can get what may be the best BBQ chicken in Colombo. We rediscovered this treat over the holidays at the Nugegoda Food City (on High Level Road).
Food City (a grocery store) sets up a grill outside certain outlets at certain times and BBQs up some amazing marinated chicken. We apologize for the lack of location photos and reliable prices (we think the chicken was around Rs. 150-200, but can't remember) but we can vouch that the nibbling is excellent.
You place your order as you go into the store (there's beef and other items, but we recommend the chicken) and by the time you get out your chicken is nicely barbecued, crispy on the outside and tender and succulent on the in. They serve it with a bunch of extraneous vegetation (lettuce, onions) and too much ketchup (which you should ask them to leave out), but the chicken is a star. It's just so tender, juicy and well seasoned. Really a treat when you can get it.