I'm the only person who eats porridge in our house and for months haven't bothered, because the amount I would now allow myself, hardly seems worth the effort.
I thought the following may be of interest to others in similar circumstances and those who would like to take a breakfast to the office or workplace.
FROM THE NIGELLA TEAM:
It is possible to make porridge (oatmeal) in advance and quickly reheat it in the morning in a microwave (or a saucepan, which will take slightly longer). We suggest using normal rolled porridge oats (in the US known as quick-cooking oats) rather than the coarser type of oats sometimes known as "Old Fashioned" oats. If you want to make just one portion in advance then it is easiest just to mix the oats with the amount of liquid suggested on the package and leave it to soak in the fridge overnight in a microwaveable container. The next morning microwave the mixture uncovered on full power (1-2 minutes, depending on your microwave) until boiling and cook for 20-30 seconds extra. Stir well before eating and add a little extra milk or water if the consistency is too thick. If you are cooking on the stove top then put the soaked oats in a saucepan and heat, stirring occasionally, until boiling and cook for 30 seconds, adding more liquid if needed.
If you want to make a larger number of portions then put the oats and liquid in a saucepan, bring up to the boil and simmer for 3 minutes. Cool and divide into portions, storing each portion in a small airtight container. The porridge can be stored in the fridge for up to 5 days or can be frozen for up to 3 months. Reheat the porridge in a microwave until piping hot and stir well before eating, again adding extra liquid if necessary.
Birchermuseli is also very popular and is made by soaking porridge oats overnight in just enough liquid to cover (you can use milk, water or a fruit juice). In the morning stir in fruit of your choice along with a little milk or yogurt.