A microwave only work with an on/off cycle. It runs on MAX for x seconds and off for y seconds. If you want 50% effect, it runs 5 seconds, then wait 5 seconds. Cooking it on low is just letting the food distribute the heat naturally for a while, instead of building up an energy bubble that will expload in steam. So low effect is good. It's still max effect but on half the time.

When cooking oatmeal porridge I usually do one cup oatmeal and 2 cups and a little more of water. In deep plate, full effect in microwave for 2 minutes but I watch it the whole time. When it starts building a volcano I let it go on until the edges of the volcano goes to the edge of the plate. THen everything is nicely cooked and I stuff my butter and a bit of salt in there and stir it until it's the thickness I want. Add milk to stop the thickeninig and eat. Maybe with some applejam on top. Oh, and make sure the oatmeal is not the generic type, it tastes nothing. There are really nice types around that makes oatmeal really great.

Of course there is a slowcook method too but I haven't tried that yet. Let the oatmeal just stand in cold water over the night, no cooking included.