Prep: Preheat oven to 350°F. Line 9x13 pan with parchment, leaving overhang on two sides.
Make crust: Whisk flour, powdered sugar, salt. Add cold cubed butter and vanilla. Work butter in until coarse crumbs form.
Bake crust: Press mixture firmly into pan. Bake 18-20 minutes until lightly golden.
Make filling: Whisk eggs and sugar 1 minute. Add flour, lemon juice, zest, baking powder, salt. Whisk smooth.
Add filling: Pour over hot crust immediately, spreading to corners.
Bake: Return to oven 20-22 minutes until edges set but center slightly jiggly.
Add coconut: Sprinkle coconut over hot filling. Drizzle with melted butter. Bake 5-7 minutes until golden.
Cool: Cool completely in pan 2 hours minimum.
Cut: Lift out using parchment. Cut into 24 bars with sharp knife. Dust with powdered sugar.