Zellers directed a lot of commercials to start his career. Having leftover sets and using rented-out equipment before it was due then got him in the habit of making short films. A prehistoric set in his possession that had been used before in a lottery commercial inspired Zellers to come up with Prometheus and Bob, pitching a pilot to Nickelodeon of an alien named Prometheus teaching Bob, a caveman, how to use fire, while documenting the teaching with a video camera. It would end with Prometheus being cooked alive by Bob, and a Monkey flying Prometheus's saucer into the camera. While the pitch was successful, the network had Zellers sign a contract saying he wouldn't show it publicly due to its very dark nature, as the installments on KaBlam! were to be more family-friendly. Prometheus and Bob would become one of the show's most popular segments, airing on all four seasons with 41 short films over 38 episodes (typically, one "tape" would be shown per episode, but three episodes of KaBlam! had two "tapes"). A live-action film was planned, but later canceled after its production stalled out.
In an animation role, Zellers has worked on Nick Jr. shows Eureeka's Castle in 1990 and Gullah Gullah Island from 1994 to 1995. He created Joey's Lunch, a series of shorts that aired as interstitials (between regular programming) on Nick Jr. From 2002 to 2003, Zellers directed and animated on HBO Family's stop motion/claymation television series I Spy, based on the children's book series created and written by Jean Marzollo and Walter Wick.