A person in our dorm asked us for a good restaurant one of the days in Cusco. One of the better restaurants we found in Cusco is LIMO Cocina Peruana & Pisco bar.
Maybe a little expensive but very good sushi.
They not only offer sushi, but a lot of different dishes, all we had time to try were very good.
The dishes start at around €10, so if you not on a very tight budget – make a visit!