Rinse lentils under cold water.
In a saucepan, combine lentils and water/broth.
Bring to a boil, then reduce heat and simmer 18–25 minutes until tender but not mushy.
Drain excess liquid and let cool completely.
While lentils cool, chop tomatoes, cucumber, onion, parsley, and mint.
In a small bowl, whisk together olive oil, lemon juice, garlic, oregano, salt, and pepper.
In a large bowl, combine cooled lentils and chopped vegetables.
Pour dressing over the salad and toss well.
Fold in feta and olives if using.
Chill 30 minutes for best flavor.
