Sprinkle in salt, pepper, cumin, and red pepper flakes.
Add the tomato paste, vinegar, and lentils. Stir frequently, cooking for 5 minutes.
Add bay leaf and pour in broth. Bring mixture to a boil.
Cover and simmer for 25-30 minutes or until the lentils are fully cooked.
Stir in chopped parsley (optional) and serve warm.