How to Make It
Cook pasta according to package directions; drain and rinse. Transfer to a large bowl.
Drain crushed pineapple over a small bowl, using a spoon to press as much juice from pineapple as possible. Add water to juice as needed to equal 1 cup liquid. Measure 1 cup of the drained crushed pineapple into a bowl; set aside. (Discard remaining crushed pineapple, or reserve for another use.)
Whisk together egg, sugar, flour, salt, and pineapple juice-water mixture in a saucepan until smooth. Cook over medium-high, whisking constantly, until mixture thickens, 5 to 6 minutes. Remove from heat; stir in lemon juice. Let cool 15 minutes.
Add chopped fresh pineapple, marshmallows, flaked coconut, oranges, reserved crushed pineapple, and cooled pineapple juice mixture to pasta in bowl; stir gently to combine. Gently fold in whipped topping. Refrigerate, covered, until ready to serve, at least 1 hour or up to 1 day.