Combine the diced pineapple and sugar in a small saucepan; bring to a boil. Cook over medium heat 10 minutes or until reduced to 1 cup. Remove from heat, and stir in rum. Cool completely; set aside.
Preheat oven to 350°.
Place gingersnaps in a food processor; process until crumbly. Add margarine and egg white; pulse 5 times or just until moist. Press crumb mixture evenly into a 9-inch pie plate coated with cooking spray. Bake at 350° for 7 minutes; cool on a wire rack 15 minutes. Freeze piecrust 30 minutes.
Place an extra-large bowl in freezer. Remove yogurt from freezer, and let stand at room temperature while the crust is cooling.
Spoon yogurt into chilled extra-large bowl; fold in pineapple mixture. Freeze 30 minutes or just until set but not solid. Spoon yogurt mixture into prepared crust. Sprinkle mixture with almonds and coconut; freeze until set. Cover with plastic wrap, and freeze 6 hours or until firm.
Place pie in refrigerator 30 minutes before serving to soften. Garnish with pineapple chunks, if desired.