Found this post on their Facebook page. All you can eat chicken and sides at participating Oporto's restaurants. Available every Monday from 5:00pm to 8:00pm, dine in only. Details are pretty sketchy at the moment, will update with list of sides available and participating restaurants as more details arise.
According to the free chicken post a couple months ago a whole chicken costs $15, so if you can down one chicken some chips and a salad looks to be good value!
Available at non Food-Court stores in WA and QLD for a limited time only, between 5pm - 8pm on Monday nights. Participating stores include Balcatta, Bentley, Bundamba, Clarkson, Canning Vale, Fortitude Valley, Heathwood, Holmview, Harbour Town, Meadowbrook, and South Perth. Available for dine-in customers only, take away is not permitted. $20 is the price per person per visit. Offer only applies to flame grilled quarter, half or whole chickens and the following sides: Chips, Spicy Rice, Crunchy Slaw, Garden Salad, Portuguese Tomato Salad and Grilled Corn. Offer excludes all other menu items including drinks. Not valid with any other offer. This offer is not available in South Australia, Sydney Football Stadium, Canberra Centre, Entertainment Quarter or Oporto stores outside Australia. The offer is available for one use per visit and is not redeemable for cash. For full terms and conditions, click on the link below.
Note: The Facebook link is only viewable to those who are in WA & QLD. The photo looks similar to this