Combine flour, coconut, and margarine; sprinkle water over surface of mixture, stirring with a fork until crumbly. (Do not form a ball.) Press into a 4-inch circle on heavy-duty plastic wrap. Cover with another sheet of plastic wrap. Roll into a 12-inch circle. Remove top sheet of plastic. Invert pastry into a 9-inch pieplate coated with cooking spray; remove remaining plastic. Fold edges under, and flute. Prick bottom of pastry. Bake at 325° for 15 minutes; cool on a wire rack.
Combine 1/2 cup sugar, cornstarch, and salt in a saucepan. Add milk, stirring well. Cook over medium heat, stirring constantly, until thickened. Beat egg and egg yolk until thick. Stir one-fourth of hot mixture into beaten egg; add to remaining hot mixture, stirring constantly. Cook, stirring constantly, 2 minutes or until thick. Remove from heat; stir in vanilla. Place banana in pastry. Top with filling.
Beat egg whites and cream of tartar at high speed of an electric mixer until foamy. Add remaining sugar, 1 tablespoon at a time, beating until stiff peaks form. Spread meringue over filling, sealing to edge of pastry. Bake at 325° for 25 minutes. Cool completely before serving.