Cut the avocados in half, remove the seeds. Remove the flesh from the skin and cut roughly. Peel garlic clove and chop roughly. Puree avocados, garlic and lemon juice. Clean the chilli pepper, carve lengthwise, remove seeds, wash and chop. Stir the yoghurt into the avocado puree. Season guacamole with salt, pepper and 1 pinch of sugar