Step 1: Rinse the lentils thoroughly under cold running water.
Step 2: Combine rinsed lentils with 3 cups of water or vegetable broth in a medium saucepan. Bring to a boil, then reduce heat, cover, and simmer for 20-25 minutes, or until tender but still firm.
Step 3: Drain the cooked lentils completely and spread them on a baking sheet to cool to room temperature. This is crucial for preventing a soggy salad.
Step 4: While lentils cool, prepare the vegetables: dice the cucumber, red bell pepper, and red onion. Halve the cherry tomatoes. Chop the fresh parsley and mint.
Step 5: In a small bowl, whisk together the olive oil, lemon juice, minced garlic, dried oregano, salt, and black pepper until well combined.
Step 6: In a large mixing bowl, combine the cooled lentils, diced cucumber, red bell pepper, red onion, and cherry tomatoes.
Step 7: Pour the dressing over the lentil and vegetable mixture. Toss gently to ensure all ingredients are evenly coated.
Step 8: Gently fold in the chopped fresh parsley, fresh mint, and crumbled feta cheese (if using).
Step 9: Serve immediately, or for best flavor, cover and refrigerate for at least 30 minutes to allow the flavors to meld. Store leftovers in an airtight container for up to 3-4 days.