Nothing will beat the free burrito which is currently still active, but the $5 burrito might be a decent alternative.
As mentioned previously by some ozbargainers, $11.50 is not worth it. However, $5 should be more manageable.
The option for the discount happens at check out. See here for sample: http://imgur.com/a/CWzxD
lunch today sorted. Thanks for the heads-up OP!