Some things I forgot to mention:
I also use cinnamon. And when I said 1/2 of a small banana, I mean really small. If it's a medium size bannana I might use 1/3. Large bannana 1/4.
Also, some forms of oatmeal are more processed than others. Quick oats are generally the most processed. Old fashioned oats are a little less processed. Steel-cut oats are less processed than old fashioned oats. And oat groats are the least processed.
Why does it matter? It matters if you are trying to lose weight or maintain your weight. Or if you are trying to control your blood sugar. Quick oats and slower cooking old fashioned oats are steamed and put through steel rollers. So the oats become "oat flakes". An oat flake has a greater surface area and therefore is digested faster, goes through your system faster, and has a greater impact on raising your blood sugar.
But steel-cut oats and oat groats may not be any better if you overcook them. The more you overcook them the faster they will raise your blood sugar and the faster they will be digested.
On the steel-cut oats, which look like little nuggets, I believe the bag suggests cooking for 20 minutes or until tender. As I said, I simmer for 5 minutes then turn off the burner and let it sit until I get everything else ready.
I suppose one could simmer for 4 or 5 minutes and then let it sit. Maybe I'll give that a try. At any rate it should be just a little chewy. That would be ideal.
Most suppermarkets carry steel-cut oats but I actually get a better deal at my local health food store. Check around if price is a concern.