Heat oven to 350°F. Grease a 9-inch square pan and line with parchment, leaving overhang.
Whisk flour, baking powder, salt, cinnamon, nutmeg, and ginger in a medium bowl.
Stir brown sugar, maple syrup, and melted butter in a large bowl until glossy.
Whisk in beaten eggs and vanilla until smooth and slightly thickened.
Fold dry ingredients into wet just until no dry streaks remain. Do not overmix.
Gently fold in diced apples and pecans. Spread batter evenly in the pan.
Bake 26–30 minutes, until the top is set and a tester comes out with a few moist crumbs.
Cool completely in the pan on a rack. Lift out using parchment overhang.
Whisk powdered sugar, maple syrup, and milk until smooth and drizzly. Adjust thickness as needed.
Drizzle over cooled blondies, let set, then cut into 16 squares.