Step 1: Preheat and Prepare
Preheat your oven to 350°F (175°C). Generously grease an 8×8-inch baking dish with butter or cooking spray, making sure to coat the bottom and sides well to prevent sticking.

Step 2: Mix Dry Ingredients
In a medium bowl, whisk together the oats, baking powder, pumpkin pie spice, cinnamon, and salt until everything is evenly distributed. Set aside.

Step 3: Combine Wet Ingredients
In a large bowl, whisk together the pumpkin puree, milk, eggs, maple syrup, melted butter, and vanilla extract. Whisk vigorously until the mixture is completely smooth and well combined with no lumps of pumpkin.

Step 4: Mix Wet and Dry
Pour the dry oat mixture into the bowl with the wet ingredients. Stir with a spatula until just combined—don’t overmix. The mixture should be thick but pourable. If adding any optional mix-ins like nuts or chocolate chips, fold them in now.

Step 5: Transfer to Baking Dish
Pour the oatmeal mixture into your prepared baking dish. Use a spatula to spread it evenly and smooth the top. Tap the dish gently on the counter a few times to release any air bubbles.

Step 6: Bake
Bake in the preheated oven for 40-45 minutes, or until the edges are golden brown and the center is set. The top should look dry and slightly puffed. A toothpick inserted in the center should come out mostly clean with just a few moist crumbs.

Step 7: Cool and Serve
Remove from the oven and let cool for 10 minutes before slicing. This resting time is important—it allows the oatmeal to set properly so it slices cleanly. Cut into squares and serve warm with your favorite toppings.