Additionally to my guide below, Tomjeh commented about an easier solution:
Start a game against any enemy you like and with all the score modifiers you want (though I would recommend to use the M-7 Lancer for yourself if you disabling thermal clip spawns).
Before starting, set the combat difficulty to "Narrative", this will make the game laughably easy.
Play through the waves 1 and 2, in wave 3 kill all enemies apart from one.
Now set the combat difficulty back to "Normal" and kill that last enemy.
This should also unlock the achievement.
I haven't tried it myself so I can't confirm that it works.
Again, special thanks to Tomjeh for pointing this out.
I found this setting quite easy to get the achievement:
- Map: Wingman
- Enemy: Reaper (need to buy with Silver Token)
Note that you can choose any enemy you want but I found Reapers to be easiest.
- Challenge: Super Elite (need to buy with Gold Token)
- Score modifier (any modifier needs to be bought with Silver Token):
That's up to you.
I used Player Damage Boost with gives you -10% of points to make it a bit easier.
To compensate that I used No Placed Ammo and used the M-7 Lancer as it has infinite ammo.
Remember that your squad has infinite ammo anyways so get them high-powered weapons.
When the match starts, turn left and run to the far corner on the lowest level.
Position yourself on the very last cover point and your squad mates on the two cover points before you.
I used Garrus and Liara while I was playing Sentinel.
Liara is very good for biotic combos while Garrus is good to get shields down.
Try to kill the enemies from a distance, that shouldn't be a problem with most enemies.
Banshees only spawn in the last wave, make them a priority.
As for the bonuses, it's up to you whether or not you're getting them. They will net you a little bonus but running for them will let your "safe zone" potentially become a spawn zone.
Apart from that, go for headshots and most importantly kill streaks.
You should be able to complete the match in less than 5 minutes for the time bonus quite easily.
I used these settings and did not go for the bonus points between the waves and got about 11.000 points while I wasn't that successful with kill streaks, so there is definitely room for improvement.