Rinse the lentils thoroughly under cold water. In a medium pot, combine the rinsed lentils, water (or vegetable broth), and 1/2 tsp salt. Bring to a boil, then reduce heat to low, cover, and simmer for 20-25 minutes, or until lentils are tender but still hold their shape. Drain any excess liquid and let cool completely.

While the lentils are cooking and cooling, dice the cucumber and red bell pepper. Finely dice the red onion. Halve the cherry tomatoes. Chop the fresh parsley and mint.

In a small bowl, whisk together the extra virgin olive oil, fresh lemon juice, minced garlic, dried oregano, 1/2 tsp salt, and 1/4 tsp black pepper until well combined.

In a large mixing bowl, combine the cooled lentils, diced cucumber, red bell pepper, red onion, cherry tomatoes, chopped parsley, and chopped mint.

Pour the lemon-herb vinaigrette over the lentil mixture. Toss gently to ensure all ingredients are evenly coated. If using, fold in the crumbled feta cheese. Serve immediately or chill for flavors to meld.