We just tried this and it is surprisingly tasty. I really like the couscous and lentil base, though I'm not sure that the arugula, tomato and feta is the exact right combination. I think you could add a lot of things to the base. It is a nice way to change up the summer menu. We used red lentils (the brand we've found is organic) and I think that they are tastier than the brown/green ones.
Here's the recipe.