Heat 3 tablespoons vegetable oil in a frying pan over medium heat. Add the onions and saute until golden. Add the flour and saute for 1-2 minutes. Set aside.
Place the lentil in a large pot and add 8 cups water. Cover the pot and bring to a boil. Reduce heat to medium and simmer for 10 minutes. Add the potato, basil, coriander, parsley, cumin, salt and pepper. Cover the pot and simmer until lentil and potato are tender (about 40 minutes), stirring occasionally.
Then add the onion-flour mixture and cook for 5 minutes. Add the beaten eggs to soup and stir constantly. Cook for 5 more minutes. If soup is too thick, add a little boiling water. Add the lemon juice, taste and adjust seasoning.