Preheat your oven to Combi Steam, 375°F/180°C, 50% (med) humidity. Grease a 9-inch square baking dish, or line with silicone paper.
Put the milk, maple syrup, eggs, vanilla and half of the butter or oil into a large mixing bowl. Whisk well to combine.
1 ¾ cups milk, ⅓ cup maple syrup, 2 eggs, 2 tsp vanilla extract, 3 Tbsp unsalted butter
Add the oats, toasted nuts, cinnamon, nutmeg, baking powder, and salt. Switch to a spatula and fold everything together well.
2 cups rolled oats, ⅔ cup pecans, 2 tsp ground cinnamon, ¼ tsp ground nutmeg, 1 tsp baking powder, 1/2 tsp fine salt
Reserve a handful or two of the berries, then scatter the rest of the berries over the base of your prepared pan (if your berries are frozen, use them straight from the freezer).
2 1/2 cups blueberries
Scrape the oat mixture over the top of the berries in the pan and smooth it out, then scatter the remaining berries across the top. Scatter the coconut flakes over the pan and drizzle with the remaining butter or oil.
2 1/2 cups blueberries, 2 Tbsp coconut flakes, 3 Tbsp unsalted butter
Bake for 25-30 minutes, until the top is nice and golden. Remove your baked oatmeal from the oven and let it cool for a few minutes before scooping or cutting into portions to serve.
Serve this as-is or with toppings of your choice (see notes for ideas). I prefer my baked oatmeal served warm, but it is also good at room temperature. To reheat, put individual portions onto plates and heat using Combi Steam, 250°F/120°C, 80% (high) humidity until warmed through (yes, you can microwave the oats if you're at work!).
Toppings of your choice