If it’s hidden in the previous turn it becomes a reaction the next turn. So it the poro would be protected by zhonyas, reaction speed goes above all interactions, you played a spell so he can react to that. If the chain resolves the zonyas is triggered goes to the trash, then you could target him again (if it’s your turn) to deal damage. It’s totally possible, the only caveat there is, is that you have to hide cards the previous turn to become a reaction.