The very first thing you should do in this level is send your engineer pods (I think you start with two) out to the flak drone in the center. If you can take control of this and keep it, the gatori won't stand a chance.
Then, you must immediately build lots of cruisers to follow after you. If you constantly build these, then you can easily fight off the pitiful little gatori attacks. Eventually, you can turn the battle around. Build an engineer pod or two heading towards the flak drone at the enemy planet. To guarantee sucess, either send multiple pods or follow the pod to distract the gatori. Once you capture the flak drone, simply sit ontop of the gatori planet as you build a transport and wait for it to arrive. After the transport is build, you can go back to building cruisers so that the gatori ships won't stand a chance when they are built.
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Horigath