@candle Yup, that’s basically it. Again, just a turn of phrase you have to get used to without real explanation.
Although you could also say « j’en mange les lundis », it’s correct as well, but feels a bit… unnatural.
(I think there’s also a veery slight nuance in meaning, but I’m not sure and am also too tired to brain it anyway)
@Shalena @candle "j'en mange le lundi" = i eat some on mondays
"i eat some on monday" like, next monday, would be "j'en mange lundi"