Oats are a slow digesting form of carbohydrate, so will give you more sustained energy than most other carb sources. So having porridge as your first meal a couple of times per week should be fine. A protein meal is better though, so have this on most days. It's worth noting, however, that adding peanut butter (or any other legumes) to grains gives a more complete amino acid profile, so you get a more useable protein source. Not as good as animal protein of course, but still decent.