Add all your ingredients except your peanut butter, optional flaxseed and milk to a zip lock bag (freezer bag).
Place in the freezer until you need it.
When you are ready to make your smoothie, remove your bag from the freezer and add the contents to your blender alongside your peanut butter, optional flaxseed and milk.
Blend away until smooth.
Pour into a glass to drink straight away or into a bottle/flask to take with you for the day.
Obviously if you just want to drink the smoothie straight away you can add everything to the blender, blend and drink!
A quarter of this recipe is low FODMAP.