Preheat the oven to 350ºF. Grease a 9" square baking dish with some melted coconut oil or ghee, or line it with parchment paper so the oatmeal doesn't stick.
In a large bowl, combine the dry ingredients: oats, baking powder, cinnamon, nutmeg, and salt.
In a separate bowl, whisk the eggs, honey or maple syrup, melted coconut oil or ghee, milk, and vanilla extract.
Add the wet ingredients to dry, and mix until combined. Stir in your mix-ins until well incorporated.
Transfer the mixture to the greased baking dish, and top with a few extra chocolate chips & some shredded coconut if using.
Bake for 35 minutes or until light golden on top & around the edges, and firm in the center. Slice into 9 to 12 squares and serve! Store leftovers in the fridge.