Preheat oven to 350°F (175°C). Grease a 9×13-inch baking dish.

Prepare the cake: In a large bowl, combine the yellow cake mix, milk, oil, eggs, and vanilla. Beat on medium speed for 2 minutes until well mixed. Pour into prepared baking dish and bake for 28–32 minutes, or until a toothpick inserted in the center comes out clean.

Make the pineapple topping: While the cake bakes, combine the crushed pineapple (with juice) and granulated sugar in a saucepan over medium heat. Bring to a boil, then reduce heat and simmer for 5 minutes, stirring often.

Poke and pour: When the cake is done and still warm, poke holes all over the top with a fork or skewer. Pour the warm pineapple mixture evenly over the cake. Let it cool completely.

Make the frosting: Beat the softened cream cheese and butter until creamy and smooth. Add powdered sugar and vanilla, and mix until light and fluffy.

Frost and garnish: Spread the frosting over the cooled cake. Sprinkle chopped pecans over the top if desired.

Chill before serving for best results.