Mash the avocado with a fork. Squeeze over a little lemon juice and mix with the avocado. This will stop the avocado discolouring, but will also add a lovely flavour to the sandwich filling.
Spread the soft avocado over the second slice of bread.
Top the avocado with the grated carrot. Season well with black pepper, then add the hummus coated top slice, face down.