I should've provided this update sooner, but here goes: I sent the basic text of my original review to Heinen's corporate and received an almost immediate reply from their local store manager who assured me that he would deal with this problem. And you know what? He did. I've gone there numerous times since and never EVER had to wait at the panini counter again. There's always someone there, bang on task and ready to go.
Unfortunately, it appears that they way they PAID for this new person was....by removing the cashier who worked at the prepared foods counter most of the time, since now there's often a requirement to go to the regular checkout registers. And that sucks, because I just asked them to heat my panini and now I'm going to stand in line with all the weekday grandma grocery shoppers and Brecksville trophy wives while my food grows cold again.
So...A for responsiveness, Heinens. D for problem solving skills.