Grease a 2-quart or 8-inch square pan with coconut oil.
In a large mixing bowl, combine 1½ cups milk, ⅓ cup maple syrup, 1 large egg, 1 teaspoon vanilla extract, 1 teaspoon pumpkin pie spice, 1 teaspoon ground cinnamon, ¼ teaspoon kosher salt, 1 cup 100% pumpkin puree, 1 teaspoon baking powder, and 2 tablespoons melted coconut oil or unsalted butter. Add in 2 cups uncooked rolled oats and optional ingredients (like nuts, chocolate chips, protein powder, chia seeds, etc.), and stir just until incorporated.
Grease a 2-quart or 8-inch square pan with coconut oil and then pour the prepared oatmeal mixture in the baking dish. At this point, you can cover the baking dish with plastic wrap and refrigerate for up to 24 hours OR just the oatmeal sit at room temperature while the oven preheats.
When ready to bake, preheat the oven to 350℉ (175℃) and if refrigerated, remove the baking dish from the refrigerator to allow it to come to room temperature while the oven preheats. Bake, uncovered, for 25-32 minutes, until the oats are set and warmed through.
Serve warm with additional maple syrup and chopped nuts, if desired.
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Notes
Egg-Free: Simply omit the egg. The oatmeal won't be as cake-like, but still delicious.Bump Up the Nutrients: Add up to 1 tablespoon each of protein powder, chia seeds, and/or ground flax if desired.Double the Recipe: Simply double the ingredients and bake the oatmeal in a 9x13 pan, adding 5 additional minutes to the bake time. Pumpkin Pie Spice: Replace with ½ teaspoon ground cinnamon and ¼ teaspoon each of ground nutmeg and ground ginger.Oil/Butter-Free: Adding a bit of coconut oil, butter, or non-dairy butter adds flavor and keeps the texture of the baked oatmeal from becoming overly dense. That said, I have omitted it many times and still enjoy the oatmeal.Storage Instructions: Store in an airtight container for up to 5 days in the refrigerator. Alternatively, slice into individual servings, wrap in parchment paper or plastic wrap, and place in a freezer-safe storage bag or container and freeze for up to 3 months. Regardless if frozen or thawed, place one serving of baked oatmeal in a heat-safe bowl and microwave in 30-second intervals until warmed through.