I know this thing heal over time but I want to have a food item of some sort to instantly heal it. Feeding waste drums to tamed tremorzilla to heal it seems like a good idea.

Shoot it with a raygun or blow it up with a nuke.

https://alexscaves.wiki.gg/wiki/Tremorzilla#Behavior

I don't see any food items that will heal the zilla in the list though.

That's because you shoot it with a raygun or blow it up with a nuke instead :)

What about feeding it with waste drums to heal it?

Not needed due to having other ways of healing.

No waste drums needed?

Correct, passive healing, and the aforementioned ways are good enough.

Sad.

Does the gamma raygun heal it even more?