Combine all ingredients in the slow cooker except for the lemon, parsley, and mint. Cook on high for 4 hours or low for 6 hours, until the lentils are tender.
Once cooked, remove about 1/3 of the soup and blend it until smooth in a blender or food processor. Return to the blended soup to the slow cooker and stir. Ladle into serving bowls, squeeze a lemon wedge over the serving and sprinkle with parsley and mint.