It's past tense.
"He cut the onion on the chopping board and put it in the oven." marked wrong. I'm getting marked wrong on what are just tiny variations in translation in this new Korean duolingo, I'm about ready to give up.
This course is in beta, so it's better to flag sentences with suggestions instead.
No one says chopping board, at least in american english.
Chopping board works too.
Why not a cutting board