In a mixing bowl, whisk together the fresh lemon juice, minced garlic, salt, black pepper, and optional chili flakes. Gradually drizzle in the extra-virgin olive oil while continuing to whisk until emulsified.

Rinse the lentils under cold water. In a medium pot, combine lentils and three cups of water. Bring to a boil, then simmer for 20-25 minutes until tender. Drain excess water.

While lentils are warm, transfer to a large bowl and mix in the prepared dressing.

Chop cucumber, bell peppers, and green onions, then add to the lentils along with parsley and mint. Toss gently to combine.

Taste and adjust seasoning with salt, black pepper, or lemon juice. Let rest for at least 10 minutes before serving.