The deal can be redeemed using the code "CHICKENSUNDAY" at checkout when ordering using the in-restaurant kiosk or through the Shake Shack mobile app or website. It's available for delivery or pick-up.
Shake Shack's Chicken Shack features a crispy-fried chicken breast filet served with lettuce, pickles, and buttermilk herb mayo on a toasted potato bun. Prices vary but it costs $9.29 for one at my nearest Shake Shack restaurant.
Photo via Shake Shack.