Cook the lentils: In a medium pot, combine the lentils and water or broth. Bring to a boil, then reduce the heat and simmer for 20-25 minutes until the lentils are tender but not mushy. Drain and let them cool.

Prepare the dressing: In a small bowl, whisk together the olive oil, red wine vinegar, lemon juice, Dijon mustard, garlic, salt, and pepper.

Combine the salad: In a large bowl, mix the cooked lentils, red onion, bell pepper, cucumber, cherry tomatoes, parsley, and mint.

Add the dressing: Pour the dressing over the salad and toss to combine. Taste and adjust seasoning as needed.

Optional: Sprinkle with crumbled feta cheese before serving.

Chill and serve: Refrigerate the salad for at least 30 minutes before serving to allow the flavors to meld.