"The man is eating a strawberry."
Translation:Ο άντρας τρώει μία φράουλα.
It doesn't sound as natural to omit "μία/μια" here. If it were for some bigger fruit (a watermelon, or even an apple, if you will), then it would be ok to drop the article. But people usually don't eat only 1 strawberry, so it would be better to specify that by sparing the indefinite article.