My girlfriend and I are no experts in Peruvian cuisine, but Tumi's food was outstanding. We had the Choclo con Queso as an appetizer (seriously, try it - it's a large-kernel Andean corn, way different than our corn, but we really liked it after a few bites). My girlfriend had the Pollo Saltado and I has the Saltado Tumi. Perfectly cooked and SO delicious, both of them.
It's a tiny dining room, far from fancy ambience, but the prices are fantastic for such good food in such ample portions. The service was polite and not pushy.
I'm craving more even as I type this - we'll definitely be going back!