"А как проходило твоё утро?" - 'cause I mean not a single morning, but all your mornings within that period.
Yes. For some reason, we prefer to avoid utilizing "утро" in plural form. Possibly, the correct question should be
А как проходили твои утра?
but to point out, that you want to know "template" of the morning processes, one inserts or impies "обычно", in which case singular утро is perfect
Как [обычно] проходило твоё утро?