Rinse lentils in a fine mesh sieve. Combine lentils and water in a medium pot and bring to boil over medium-high heat. Reduce heat to medium-low. The lentils should gently simmer until tender (stirring occasionally), approximately 30-35 minutes. Drain lentils and let cool at least 10 minutes.
While the lentils are cooking, dice all the vegetables, then combine with the cooled lentils.
Whisk together dressing ingredients in a small bowl until thoroughly combined.
Drizzle dressing over the lentils and vegetables and toss to combine.
Transfer to individual bowls or a serving platter. If desired, you can optionally garnish with a sprinkle of additional parsley and feta cheese.