The quickest way to defeat the Guardian at Orion is to have the Plasma Cannon. Refit or build either Battleships or Titans with nothing but Battle Pods, Damper Field (if you've already had run-ins with the Antarans), Reinforced Hull (Achilles Targeting Unit ignores armor), and as many Heavy Plasma Cannons that can fit (8 to 12 is possible if you've acquired Megafluxers). 3 or 4 ships is all that is needed; Guardian will have a "warp core breach" (large, blue explosion) on the second or third ship. Keep doing this until you have the desired Tech. Don't forget to save a space in your Ship Leaders for Loknar, as he has excellent stats (Ship Officer Dalan has the same stats, but without the Galactic Lore)

The Ideal tech to get off of Orion is the Black Hole Generator, Reflection Field, and the Spatial Compressor (the first 2 because you can only get them off of the Antaran Titans, and the third you can get off the cruisers), and the Death Ray (which you get all the time from Orion anyway, but can only be gained off the Antaran Battleship or Titan, not before)