Plants vs. Zombies Garden Warfare 2

This achievement is really simple if you wish to get it done quick.

Step 1: Spawn in as rose.
Step 2: Head to the middle of the map and raise the flag
Step 3: Wait for the zombies to bunch up around you
Step 4: run around the flag and turn them into goats.
Step 5: Wait on your cool downs and repeat step 4

Note: Try to stay inside the circle If you leave it to many times the zombies will claim it and you'll need to restart.

I will be putting up a video once I get the clips :) Hope this helps.
If there is anyway I can improve this guide please let me know!

As ayerow said, if you use the flag of power, you can do this on the browncoats round and wait till the goats have turned back in to zombies.

I jumped onto the flag Base to avoid the zombies melee'ing me, they throw rocks but never enough to cause any serious damage, and just played the waiting game.

UPDATE: Forgot to add that you can use the same zombies and it still counts

Another option besides what Ayerow mentioned is to do a Garden Ops as the Rose. Her Goat ability has splash damage so using her Slow you can catch a bunch together. I got 21 just in on of the Story Mode Ops.