"You have already eaten lunch"
Translation:Umekwisha kula chakula cha mchana
That's also OK.
The -mesha- prefix comes from the verb kwisha, which is a bit like kwenda in that it sometimes keeps the kw... but it's also been weathered down and when it drops the kw it also drops the i, so there's:
It's a pretty big oversight to expect us to type it the first way when, throughout the rest of the unit, the third way is being taught. But that's why the course is in Beta