Preheat the oven to 180°C conventional heat or 165–170°C fan.

Grease or line an 18 × 18 cm baking dish or approximately 20 cm round dish.

For a cake-like texture, blend the oats into oat flour. For classic baked oatmeal, leave them whole.

Mash 240 g ripe banana until mostly smooth.

Add 180 ml milk and whisk to combine.

Stir in cocoa powder, baking powder, and an optional pinch of salt.

Add the rolled oats or oat flour and mix thoroughly.

If using whole oats, let the mixture stand for about 5 minutes.

Fold in 30–40 g chocolate chips if desired.

Transfer the mixture to the prepared baking dish and spread evenly.

Sprinkle with extra chocolate chips and chopped nuts if desired.

Bake for 20–25 minutes.

The center should be set and a toothpick should come out without raw batter. A few moist crumbs are fine.

Let the baked oatmeal rest for about 10 minutes before serving.

Serve warm, chilled, or refrigerate for meal prep.