Preheat oven to 150 C/ 140 C (fan) and place a silicone baking mat or piece of baking paper on the bottom of a large baking tray.
Place the peanuts into a blender and pulse until they are coarsely chopped.
Add the oats, sugar and salt to the chopped peanuts and pulse again for 10 seconds or so until everything is mixed and the oats are chopped but still have some texture.
Whisk the peanut butter into the sunflower oil until smooth.
Whisk the egg white until light and frothy, and stir in the peanut butter and oil.
Add the oat mixture to the egg white mixture and stir to coat well.
Spread out on a single layer on the baking tray and bake for 20-25 minutes, stirring once or twice, until the granola is light golden and holding shape well.
Leave to cool on the baking tray and then stir in the coarsely chopped dark chocolate and the marshmallows.
Store in an airtight container.
Notes
127 kcal per 25 gram serving. See below for detailed nutrition information as analyzed by My Fitness Pal.