I have a set of nesting glass containers like this that only cost like $40 for the whole set. You can probably find similar sets for cheaper; that was the first google result I found.
Just dump the contents from your plastic container into one of those and voilà – no more nanoplastics. :)
e: oh, it just occurred to me you weren’t talking about reheating in their packaging, but how it’s served. I suppose if it were me and I knew them well, I might try to gently mention to them that their packaging isn’t great, and maybe suggest they look into a paper-based option instead. More likely I’d puss out and never say anything, because I’m a social coward. Best of luck to you, and I’d say never reheat in the package they give you.