I have a series of hard days in my near future. I want to prepare quick and easy lunches. I have the idea of taking lentils putting them trough a blender to get lentil flour. If you add the lentil flour to a thermos flask add salt and spices and add boiling water. Could you then have lentil soup of some sort to help you get trough the day? You would off course preheat your flask. Would it better to prepare the lentils on the morning you consume them or is it possible to do this the previous evening? If the soup is only luke warm after 12 hours in the flask it is OK. Even if it is cold a minute or two in the microwave is still OK. What would be the best way to do thermos cooking? 
In general, when using a thermal cooker, the basic procedure is this:  Start some water boiling Bring your soup base to a boil (separately) Pour the boiled water into your insulated flask Make your soup and let it boil for a few minutes (fully cook any meat, typically, but not more than 5 minutes) Dump the water out of your flask (it was just to pre-heat it) Pour the soup into the flask with any items that shouldn’t be boiled and seal it Wait a few hours Eat  You can find recipes by searching for ‘thermal cooker recipes’, but some are for appliances which have their own cooking element in them, so don’t require the pre-heating step.  You can also try searching for ‘soup bento’ recipes to try to find something similar to base your initial ratios on, and then adjust from there to your taste and time delay. 