One of the ways I'm doing this is finding foods that I can make large batches of relatively cheaply, and then freeze them in smaller portions so I can just heat & eat later. Not everything does so well this way, but I've found that most rice & veggie dishes do.
This one is delish! Easy to make! And freezes well. Plus, even with all the veggies, you can usually make 3 or 4 portions (depending on how many servings each) at a relatively low price. If you grow your own food, you can make it even cheaper.
Then just toss your frozen portion with a little water in to a Wok or Skillet and heat to serve. It's that simple. Lunch - or Dinner - in seconds!