Anytime I lack the time or energy to make a full-on meal, I tend to fall back on pasta. It's quick to make, and even better, nearly foolproof to execute.
Of course, just because it's easy doesn't mean it has to be boring! If you have fresh tomatoes on hand, you can make homemade sauce in less than ten minutes. It'll take at least that long to boil the water and cook the pasta, so why not make fresh sauce instead of opening a jar?