Whisk pudding mix with 1¾ cups cold milk for 2 minutes until thickened. Let stand 5 minutes. Pour into graham cracker crust, smooth the top, and refrigerate for 30 minutes.
In a saucepan, heat evaporated milk, sugar, butter, and egg yolk over medium, stirring constantly, until thick and bubbly (7–10 minutes).
Boil 1 minute, then remove from heat. Stir in vanilla, coconut, and pecans. Let cool for 10–15 minutes, stirring occasionally.
Spoon the warm topping over the chilled pudding layer. Spread evenly with a spatula.
Refrigerate for 2–3 hours until set. Serve cold with whipped cream, chocolate curls, or toasted pecans if desired.