Unfortunately, there currently isn't a Strongholds playlist to easily get this achievement.
That being said, it's still possible to earn by playing in the "Team Arena" or "Solo/Duo Queue Team Arena" Ranked Arena Playlists. However, the playlists mentioned contain a mix of Slayer, Capture the Flag, Strongholds, and Oddball. So 75% of the time you're unfortunately not going to have the game type needed. It's not the greatest option in the world, but it's there.