Heat oil in a large saucepan over medium heat. Add onion and cook for 5 minutes, or until soft. Add garlic, carrot, pumpkin, lentils, stock, 2 cups water and tomatoes.
Bring to the boil, reduce heat and simmer, covered, for 30 minutes or until pumpkin is very tender.
Remove from heat and puree using a stick blender.
Meanwhile, toast bread and top with sliced avocado. Sprinkle soup with parsley, dollop with yoghurt and serve with avocado toast.