Just a reminder: Mondo Burger had a sauce too!
Remember in the scene where Dexter gets fired because he couldn't assemble the burger as fast and clean as everyone else? Remember the henchman yelling;
"Bun, patty, tomato, sauce, cheese, lettuce, pickles, bun Assemble!"
Did you hear him say sauce? Yes he did, he said sauce. Mondo had the white sauce while Good Burger had the orange sauce. Although there are no close ups of the burgers assembled except for Dexter making a mess so the sauce goes unnoticed. I assume it would be white since you can't really see it on camera, so I guess that Mondo Burger had a sauce that's similar to ranch dressing or Cesar dressing.