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