Onion joined the academy staff after spending two seasons with Chicago FC United, where he worked across 6 different age groups. Previous coaching experience includes time as a college assistant with both Nebraska Wesleyan University and Benedictine University. While in Nebraska, he was in charge of two 2005 age groups at Villarreal Nebraska Academy. Other experiences include time with Chicago Empire - South as Head Coach of a U16 group, as well as coaching for Everton FC Soccer Schools. During the 2020 USL Championship season, he was a 1st team Opposition Analyst & Video Scout for Colorado Springs Switchbacks FC. While with Switchbacks FC, he worked directly with Alan Koch, former MLS Head Coach at FC Cincinnati during their expansion season.

After joining the academy staff, Onion was the interim Head Coach for the U13 academy group for 4 months. During the 2022/23 season, he worked as the assistant coach for the U13 & U14 age groups, and during the 2023/24 season, he has been the U13 & U17 assistant coach.

He holds a USSF B License as well as a UEFA B License through the Scottish FA.