I always start by turning my oven on to 350°F so it's fully heated by the time my batter is ready. This step matters more than people think, since a cold oven can leave the center undercooked. While it heats up, I grease my ramekin lightly with butter or oil. It only takes a minute but saves you from a stuck, crumbly mess later.
In my mixing bowl, I add the rolled oats, baking powder, cinnamon, chia seeds, and a pinch of salt first. Stirring the dry stuff together before adding anything wet helps the baking powder distribute evenly. This little trick keeps the oatmeal from rising unevenly in one spot. It only takes about 15 seconds of stirring.
Next, I pour in the milk, nut butter, maple syrup, and mashed banana if I'm using it. I whisk everything together until the batter looks smooth and there are no dry oat clumps left. If I'm adding protein powder, this is when it goes in too. The batter should look thick but pourable, almost like pancake batter.
Once everything is combined, I pour the batter straight into my greased ramekin. I like to give it a gentle tap on the counter to release any air bubbles. If I have extra fruit or nuts on hand, I'll sprinkle a few on top right before it goes in the oven. This is also the moment I add a few extra chocolate chips if I'm feeling indulgent.
I slide the ramekin onto the middle rack and bake it for 25 to 30 minutes. I know it's done when the top turns golden and a toothpick inserted in the center comes out clean. If the top looks like it's browning too fast, I loosely tent it with foil. Every oven runs a little different, so I check around the 22-minute mark.
Once it's out of the oven, I let it sit for about 5 minutes before digging in, since it's very hot right out of the gate. This short rest also helps it set a bit more so it doesn't fall apart when I scoop it. I usually top mine with a drizzle of nut butter and a few banana slices. Then it's finally time to enjoy the payoff of five minutes of prep work.