Rinse the lentils well, then place them in a large pot with the diced onion, olive oil, and salt. Add hot water to cover, cover the pot, and simmer over low heat until the lentils are fully cooked, adding more water as needed.

Blend the lentils using an electric mixer or blender until smooth.

Strain the soup through a fine mesh strainer, then stir in the cumin, lemon juice, and chopped parsley.

Serve hot with fried bread cubes.