Find a Brightly Colored Egg.
Brightly Colored Eggs can be found during Noblegarden in various low-level populated villages.
Bloodhoof Village is popular due to its large open spaces and Fairbreeze Village is popular for its density. Razor Hill is okay but there are more obstacles to navigate around. Brill is not very popular because the eggs can be difficult to reach and it feels like fewer eggs spawn there than in the other villages. Naturally, your egg-grinding experience may vary by realm.
I can't speak to popularity for Alliance since I predominantly play Horde. Feel free to reply with your own experience or opinion.
The easiest achievement for all of Noblegarden, only requires you to collect a single Brightly Colored Egg.