Go to the main node in order to get the warmonger. You can also use two platforms to reach the node with your fast hoverboots. Using three platforms is indeed a waste of time. Restarting for that is good idea because it's the beginning of the run.

Go to the first key node. You have to kill the first grungarian at the left and two turrets at the right and then the shield. Then one shoot should kill the three next turrets, and one other for the second field. Then you will need 3 or 4 shots to destroy all the grungarians and the shield. Activate the key node.

Go to the planetary defence center. A shortcut allows you to win 1 or 2 seconds but it is hazardous and not that effective. Spam warmonger (melee attacks are probably a waste of time, even if it's harder). Activate the planetary defence center by destroying the two shields with two shots of warmonger.

Initiate reboot sequence as fast as possible. This sequence is easy : you have a lot of time to get weapons (doppels, thundersmacks, groovitron and why not zurkon). When there will be a monster, kill it as fast as possible and kill the last grungarians at the right, anticipating with doppels for instance. Then level ends.