Preheat oven to 350°.
To prepare crust, place first 4 ingredients in a large bowl; beat with a mixer at medium speed until well blended. Lightly spoon flour into dry measuring cups; level with a knife. Add flour to sugar mixture, beating until mixture resembles coarse meal. Press into bottom of a 13 x 9-inch baking dish coated with cooking spray. Bake at 350° for 12 minutes or until lightly browned; cool on a wire rack. Set aside.
Lower oven temperature to 325°.
To prepare topping, combine 4 egg whites, cream of tartar, and salt in a large bowl; beat with a mixer at high speed until soft peaks form. Gradually add 1 cup sugar, 1 tablespoon at a time, beating until stiff peaks form. Fold in 1 cup flaked sweetened coconut and 2 1/2 teaspoons grated lemon rind; spread evenly over prepared crust. Bake at 325º for 40 minutes or until top is dry and lightly browned. Cool completely on wire rack. Cut into 32 pieces. Store in an airtight container.