This achievement would be easiest in roses story-line, She has a mission where you have to fight a giant goat and in this mission there are tons of goats. Just play as a chomper and eat one. But make sure to burrow than swallow the goat. Just chomping the goat will not work!
I will update with the mission once the game releases.
Edit: Thank you tornprince for notifying me you can start a private match and set your team as roses and yourself as a chomper. To easily get this achievement