How to Make It
In a medium saucepan, cover the lentils with water and bring to a boil. Simmer over moderately low heat, stirring occasionally, until tender, about 30 minutes. Drain.
Meanwhile, bring a medium saucepan of salted water to a boil. Add the arugula and blanch for 30 seconds. Drain and rinse under cold water. Squeeze out excess water and transfer the arugula to a food processor. Add the parsley, tarragon and mint and process until finely chopped. Transfer the puree to a colander and squeeze out any excess liquid. Transfer the puree to a large bowl.
Stir the yogurt, shredded cucumber and lentils into the arugula puree and season with salt and pepper. Transfer to small bowls and serve.