01 - Preheat oven to 350°F. Grease an 8×8-inch baking dish with butter or non-stick spray.
02 - In a large mixing bowl, whisk together the rolled oats, cinnamon, nutmeg, baking powder, and salt until evenly distributed.
03 - In a separate bowl, whisk together the eggs, milk, maple syrup or honey, and vanilla extract until smooth and well blended.
04 - Pour the wet mixture into the dry ingredients and stir gently until just combined, being careful not to overmix.
05 - Gently fold in the grated carrots, chopped nuts, raisins, and shredded coconut if using, distributing them evenly throughout the batter.
06 - Pour the mixture into the prepared baking dish and spread it out into an even layer using a spatula.
07 - Bake for 35 to 40 minutes until the center is set and the top is lightly golden. A toothpick inserted in the middle should come out clean.
08 - Allow the baked oatmeal to cool for 10 minutes before slicing into portions and serving warm.