Rinse the mixed lentils under cold water.
In a medium pot, bring 2 cups of water to a boil. Add the lentils and cook for 15 minutes or until tender. Drain and set aside to cool.
In a large bowl, combine the cooked lentils, cucumber, bell pepper, carrot, red onion, parsley, and feta cheese.
In a small bowl, whisk together the olive oil, lemon juice, salt, and pepper. Pour the dressing over the salad and toss to coat.
Serve the mixed lentil salad chilled.