Ulysses eats oatmeal on a near-daily basis and I eat a fair bit of it too. We prefer the texture of stovetop oatmeal but don't want the hassle of cooking it daily, so we make a medium-sized batch and microwave it.
I never thought to even try microwaving oatmeal until I saw a recipe by Mark Bittman. Turns out it works great!
Put everything in a saucepan. Cook, stirring occasionally, until the mixture reaches a boil. Turn heat down so molten oatmeal doesn't spatter everywhere, and cook for 5-10 minutes. Cool before refrigerating. It will take on a pudding-like texture in the fridge.
This recipe makes a pretty sweet oatmeal, which is how I like it.
For our microwave, a half-cup portion takes 45 seconds to warm. A smaller portion takes 30 seconds.