Alright, I may be wrong. Although, I can't get passengers to work the way they should, even though I'm using the same exact format as a command. So, I am trying to spawn a Phantom, with the passenger being a zombie. The vanilla command for this is:

/summon phantom ~ ~1 ~ {Passengers:[{id:"minecraft:zombie"}]}

So, my .setData looks like this:

.setData({
Passengers:
	[{id:"minecraft:zombie"}]
})

)

(Pastebin of the full .zs file: https://pastebin.com/5KWHhsFe)

The phantom spawns, but it will not spawn with a passenger. Is this a limitation of Zen Summoning/CraftTweaker or am I just an idiot? I'm more inclined to believe it's the latter, but I'm having trouble finding documentation on CraftTweaker for my specific use case. If it's not a bug feel free to close, but I would really appreciate a link to some documentation to figure out what I'm doing wrong or tips on what to fix, thanks!

Looks like passengers require custom support beyond deserializing NBT. I've copied the logic used by vanilla, your script should work as-is on the latest build
https://www.curseforge.com/minecraft/mc-mods/zen-summoning/files/3633674
Thanks for the feedback!

Awesome, just tested it out and it works perfectly now. Thanks for the fast response and fix!