In a medium bowl, combine lemon juice, minced garlic, salt, pepper, and optional chili flakes. Whisk and drizzle in olive oil while whisking until emulsified.

Rinse lentils under cold water and combine with 3 cups of water and a bay leaf in a large pot. Bring to a boil, then simmer for 20-25 minutes until tender. Drain and discard bay leaf.

Transfer warm lentils to the bowl with dressing and fold gently to coat. Let cool slightly.

Chop cucumber, bell peppers, and green onions. Once lentils are cool, add fresh vegetables, parsley, and mint. Toss gently to combine.

Taste and adjust seasoning with salt and pepper. Serve immediately or chill for 30 minutes before serving.