If you’re tempted to add sliced frankfurters to this soup, please don’t.
Wash and drain the lentils. Cover with the water and simmer for 1-½ hours. Saute the onion in the olive oil until golden. Add the onion and oil to the lentils and stir in the salt. Cook gently for one hour.
Wash the spinach thoroughly and chop up, not too fine, and add to the lentils. Simmer for 15 minutes and then stir in the lemon juice.
Serve with a paper-thin slice of lemon in each bowl.