You -- yes, you! -- can win a $25 gift card to Hwy 61 Roadhouse and Kitchen (34 South Old Orchard Avenue, Webster Groves; 314-968-0061). All you have to do is tell us where we ate this sandwich. Sorry for the strange angle. Consider it an added degree of difficulty.
Rules: To be eligible, you must leave a valid e-mail address (or Twitter handle or Facebook profile URL) in the comment-entry field. One guess per e-mail address. Employees of the restaurant in question and Riverfront Times are not eligible.
Update: Congrats to christinewolfe, who correctly guessed that this sandwich -- more specifically, this torta -- is from Laredo on Lafayette Square (2001 Park Avenue; 314-231-9200).
Hint #1: New face, old place.
Hint #2: You probably wouldn't refer to this sandwich as a sandwich.