For National Mushroom day Smashburger has the Truffle Mushroom Swiss Burgers (any kind) for $4, online you can choose the required meat (eg: grilled chicken or fried chicken) and after discount it will be $4, you can order any number burgers in one order. Expires 10/15
Also can place future order today, say to pickup for lunch or dinner for tomorrow and you will see the discount.
https://smashburger.com/