Preheat oven according to cake mix directions. Grease a 9×13 inch baking pan.

Prepare cake according to package directions. Pour batter into prepared pan and bake as directed until a toothpick inserted in center comes out clean.

While cake is still warm (but not hot), use handle of wooden spoon to poke holes all over cake, about 1 inch apart.

While cake is baking, spread pecans on baking sheet and toast in oven for 8-10 minutes until fragrant.

In a medium saucepan over medium heat, combine sweetened condensed milk, butter, and brown sugar. Cook, stirring constantly, until butter melts and mixture is smooth and slightly thickened, about 2-3 minutes.

Remove from heat and stir in toasted pecans, coconut, vanilla, and salt.

While filling is still warm, slowly pour it over cake, directing it into holes. Use a spatula to gently spread filling, ensuring it seeps into holes while creating a layer across top.

Allow cake to cool completely to room temperature.

For optional topping: Place chocolate chips in heatproof bowl. Heat heavy cream until just simmering, then pour over chocolate. Let sit for 2 minutes, then stir until smooth.

Pour ganache over cooled cake and spread in even layer. Sprinkle with additional coconut and pecans if desired.

Refrigerate cake for about 30 minutes to allow ganache to set before serving.