In a large bowl, combine the drained pineapple, sweetened condensed milk, pecans, and lemon juice. Stir well to combine. Fold in the whipped topping.
Transfer the filling to the graham cracker crust and spread it into an even layer. Refrigerate for at least 4 hours up to 24 hours before serving.
Garnish with more whipped topping, chopped pecans, and Maraschino cherries, if you like.
Notes
Drain the pineapple very well. Otherwise, the filling can become too watery to set up. To drain, place the pineapple in a fine mesh strainer (preferably over a bowl). Use a silicone or rubber spatula to press down on the pineapple to push out as much juice as possible. Stir the pineapple and continue to press it through the strainer several times until almost only a small amount of juice comes out when pressed.