The food pyramid is just a guideline and subject to change. What do you mean with one meal? You eat only once a day, with the exception of a candy bar?
There is a saying: "Eat breakfast like a king, lunch like a prince, and dinner like a pauper", there's probably truth in that: your body needs energy throughout the day and it's best to consume most of it early in the day so that it will be useful immediately.
If you're having trouble finding time to cook you can make a big batch of food and freeze it so that it can last several days. Do vary your diet to get the required nutrition.