Place veg, stock cubes, herbs and spices in the slow cooker. Cover with water, then sprinkle over lentils to just cover the liquid. (Add more if you like a thicker soup, or less if you prefer thinner soup.)
Cook on high for 4 hours or low for 6 to 8 hours.
Blend with blender to the thickness you like or use a masher. Add cream if desired.