Preheat oven to 275F. Line a 9Ã—13-inch bakng pan with parchment or spray with non-stick spray.
In a medium mixing bowl, beat flour, butter, and brown sugar until combined. Press the mixture into the prepared pan. Bake for 10 minutes; remove from oven.
To make the filling:
Increase oven temperature to 350F.
In another medium mixing bowl, beat together eggs, brown sugar, and vanilla until light and fluffy. Sift in flour and baking powde; beat until just combined. Use a rubber spatula to fold in pecans and coconut.
Pour the filling over the crust. Bake for 20 minutes or until set.
To make the glaze:
Whisk together powdered sugar, melted butter, and lemon juice.
Drizzle glaze on the bars as soon as they come out of the oven.