As my niece told me: “How can you have meatballs if there’s no meat inside?”
To a certain degree I had to yield to her reasoning. If there’s no meat you should call them “[something]balls” not meatballs.
Two incongruous words paired together, what a headache to explain to kids. With these lentil ‘meatballs’ however the resemblance and taste to meat is so close that there’s no better way to describe them besides ‘meatballs’.
That’s why the oxymoron is justified. Just this one time.