In a large measuring cup, soak the oats in 3/4 c. Greek yogurt and 2 Tbsp. milk for 10 minutes.
Meanwhile, in a large bowl, whisk together whole wheat flour, baking powder, baking soda, cinnamon, nutmeg, and salt.
To the dry ingredients, add the soaked oats, the remaining 1/2 c. Greek yogurt and remaining 4 Tbsp. milk, the egg, melted butter, and brown sugar. Stir until just combined.
Heat a griddle over medium heat and spray with cooking spray. Use a 1/4 cup measuring cup to scoop batter onto griddle. (You may have to use a greased spatula to flatten the batter a bit.) Cook about 3 minutes per side, or until lightly browned. Serve immediately.