Place lentils in a large pot and cover with water or stock (approx. 4 1/2 cups). If using water, flavour with soup mix. Cover pot and simmer for 30 minutes or until lentils are cooked through.
While lentils are cooking make croutons: Cut bread into small cubes. Coat the bread pieces with oil, salt & spices. Fry on med heat until crispy and golden brown on all sides. Lay on paper towel until ready to use. This will soak up some of the excess oil.
Dissolve cornstarch in 1/2 cup of cool water.
Add dissolved cornstarch, salt and margarine to lentils. Cook for 5 minutes longer, stirring constantly. Soup with thicken.