Which behavior(s) can't be done by non conscious entities?
For example, summarize its own experiences for the previous day in a few sentences.
Oops, wait, have I cheated? I said "experiences," and a non conscious entity (such as a posited p-zombie) by definition has no experiences.
Well, no, I haven't cheated, because whether the p-zombie has subjective experiences or not, being able to recall for instance things it perceived and things that happened to it and things it did and why it did them, and summarize those recollections in narrative form, is something that a conscious person can do, so it's something that a p-zombie should also be able to do as well. That is, the p-zombie must at least be able to fake recounting its (nonexistent) experiences.
My hypothesis is that the processing and remembering and recalling and summarizing it has to do in order to fake narrating its experiences, is indistinguishable from actually having experiences. By indistinguishable I don't mean we can't tell the difference (which is what we started out inherently assuming), I mean there is no difference. Which makes our posited p-zombie conscious, and therefore not a p-zombie.
Note that all that necessary processing etc. is integrating a lot of information, so other hypotheses that approach the question of consciousness more from the point of view of the nature of the processing itself are not necessarily incompatible with this view. I'm not looking at the hardware but at the software design specs: what does consciousness do, and why? The value of being able to summarize interactions with the world into high-level chunks, narratives of things and beings and the self taking actions for reasons, should be self-apparent. Memory, learning, thinking, planning, and the use of language are all either aided or made possible in the first place.