Prepare the lentils: Rinse the lentils under cold water. In a pot, combine the lentils and water. Bring to a boil and then simmer for about 15-20 minutes, or until tender. Drain and set aside to cool.
Make the dressing: In a mixing bowl, whisk together the lemon juice, olive oil, oregano, salt, and pepper until well blended.
Combine the salad: In a large bowl, add the chopped spinach, romaine lettuce, and cooked lentils. Pour the dressing over the salad and toss gently to coat.
Serve: Garnish with the fresh mint leaves and, if desired, radish slices and crumbled feta cheese. Serve with lemon wedges on the side for an extra zesty kick. Let it rest for about 10 minutes before serving to allow the flavors to meld.
