Basically you need only two things: fully upgraded Light Energy Forces unit...

...and one of the Cricket type weapons, also fully upgraded

NOTE: If you didn't have any luck finding one of those in lootboxes, you can grab one on level 36 (top bushes on the map, just place anyone right near the chest to destroy it)

First of all put Cricket in the main weapon slot of the LEF unit, just like here (it's important because we want to start with Cricket and we're not planning to buy anything else during the fight)

And that's it! Start the mission, place one LEF unit like here...
...and he will do all the work for you

NOTE: Light Energy Forces is so overpowered that you can complete the mission even without firing the orbital laser, but with a tiny bit of RNG involved (that's because after the big robot is destroyed it spawns a small alien operator and he is invincible for a couple of seconds so he can rush to the exit)