"Unakula viazi?"

Translation: Do you eat potatoes?

[Yobebo4]

wouldn't it be 'wala viazi?'

[AGreatUserName]

That's the aorist tense (also called simple present, although it's not always present) which is not taught at all in this course. It mostly seems to occur in news headlines in the written language, but I still find it strange that it's not taught at all in Duolingo.

Unakula is the present tense (also called continuous, although it's not always continuous).