In a medium saucepan, combine lentils and water (or broth).

Bring to a gentle simmer, then reduce heat and cook 20–25 minutes, until al dente.

Drain in a colander and rinse under cold water. Transfer to a large bowl.

In a small bowl or jar, whisk together olive oil, red wine vinegar, lemon juice, Dijon mustard, salt, and black pepper until emulsified.

To the bowl of cooled lentils, add red onion, cucumber, bell pepper, cherry tomatoes, and olives.

Pour dressing over the salad and toss gently to combine.

Fold in crumbled feta cheese, parsley, and oregano.

Taste and adjust seasoning, adding more salt, pepper, or lemon juice if desired.

Let sit 10 minutes for flavors to meld. Serve at room temperature or chilled.