The sequence is set up with 2 cannons on the ground level and 2 cannons on the top walkway. 2 soldiers man each cannon. When the sequence starts, immediately fly directly over one of the ground cannons and fire (X). This will kill both soldiers. Continue to hover right there without moving. 2 more soldiers will spawn and run over to the cannon. When they get within range, fire again. 2 final soldiers will spawn, so kill them. Repeat this process with the other ground cannon, then with the two upper cannons. There are 6 soldiers total for each cannon.

If you're having issues getting hit while hovering over a cannon, position yourself a little behind it. The lunar blast has pretty good reach on it, so you'll still be able to kill both soldiers.