Preheat oven to 400 degrees F and line a baking sheet with parchment paper.
Combine pretzel pieces, pecans, melted butter, and brown sugar in a large bowl and mix until well combined.
Pour pretzel mixture onto the prepared baking sheet and spread into an even layer. Bake for 7-9 minutes, then allow to fully cool.
In a large mixing bowl, beat cream cheese until smooth. Add in pudding mix, milk, and sugar. Continue mixing until mixture thickens.
Fold in 1 tub of cool whip and both cans of drained pineapple, then spread cream mixture in a 9×13-inch pan.
Spread the remaining tub of cool whip over the top, then sprinkle with the pretzel mixture.
Chill until ready to serve and garnish with additional pineapple if desired.