In a medium size saucepan, combine the broth and lentils over medium-high heat. Bring to a boil, reduce to low, cover, and simmer until the lentils are tender and the liquid is absorbed. Remove from heat and cool completely.
Once lentils are cool, combine with cucumber, tomatoes, olives, onion, dill, parsley, and feta (if using) in a large bowl. Toss to combine.
In a small jar with a tight-fitting lid, combine the olive oil, vinegar, oregano, salt, pepper, and lemon juice. Close and shake until well-combined.
Pour dressing over the lentil mixture, and toss to coat. Serve immediately, or refrigerate for at least an hour to allow the flavors to meld.