Optimus Prime, Gleaming Commander attacks Private Lionizer, knocking him out. Lionizer changes to RS Firesteel Saber, onto another of my characters, but Optimus Prime triggers his bot mode ability, and uses it to transform Prowl, Strategic Mastermind in my opponents KO area, which then transforms to Prowls bot mode and triggers his bot mode ability to remove a weapon. My opponent scraps RS Firesteel Saber. This all happened as a result of my opponents attack- is this the correct order of play?

Not quite. There are two errors in the scenario youre describing. The first is that Optimus trigger will resolve before damage is dealt to Lionizer. The second, is that your Optimus can only choose characters in your KO Area, so you would not be able to flip any characters in your opponents KO Area.

Source: Wizards of the Coast (2019-08-23)    【Link to Ruling】

Tags: Optimus Prime, Gleaming Commander