In a medium pot heat the olive oil and sauté the onions until translucent, about 5 minutes.
Add the mushrooms and sauté until liquids have evaporated. Add the lettuce and spinach and continue sauteing for 2-3 minutes. Add about 1 ½ cup water, ¼ tsp salt and simmer for 15 minutes.
Add the dill and heat for 1 more minute. Remove from heat and set aside. Remove 2 tablespoons of the broth/cooking water and set aside.
To make the tahini sauce mix 2 tbsp tahini with 1 ½ tbsp lemon juice mix until it turns white, add 1-2 tbsp of the saved cooking water, and mix well.
Add the tahini-lemon mixture gradually to the soup and mix gently until blended well. Heat the soup slightly at low heat-before serving.
To serve place soup in in a shallow bowl, squeeze some lemon, add black ground pepper. Add a few homemade croutons on top for some extra crunch.
Notes
Once cool, store in a closed container for up to 3 days. To reheat, place over low heat until warm. Do not bring it to a boil.