Red lentils are one of the cheapest foods around. They don't have a lot of flavour, are not particularly glamorous and many people walk right past them in the supermarket. However red lentils are one of my favourite and most used ingredients.
 
While you can make red lentil focussed meals, one of the main reasons I value red lentils is actually for their flexibility and blandness. You can slip them into much of your cooking, with little serious effect on the final flavour. However by adding in a few tablespoons or quarter cup of red lentils you are boosting the nutrition of the meal you're making

 

 

 

An example of this is the Sweet Potato and Lime Soup I cooked on the weekend. The basic recipe was for a purely vegetable based soup. Lovely flavours, but with little protein I knew it would not be filling enough to make a meal. The mere quarter cup of red lentils I added was not enough to change the flavour, but it did add nutritional complexity and oomph.
 
A trick I've learnt from UK Dietician Emma Carder is to add a tablespoon of red lentils to pasta. Simply add it to the boiling water, at the same time as the pasta. The red lentils cook quickly and are barely noticeable in the final dish.  It's a great addition.