Preheat oven to 350. Spray 12 cup bundt pan with cooking spray.
Drain pineapple; measure 3/4 cup juice to use with cake mix and reserve rest for soaking mixture.
Beat cake mix, pudding mix, eggs, oil and 3/4 cup of juice in large bowl of electric mixer for 2 minutes. Scrape half vanilla bean pod; combine with cake batter or mix 1 T vanilla extract into cake batter.
Pour into prepared pan. Bake 38-42 minutes or til toothpick inserted near center comes out clean.
Combine remaining pineapple juice, powdered sugar and melted butter in a small bowl while cake is baking. Scrape other half of vanilla bean and mix with juice or stir in remaining 1 T vanilla extract.
Remove cake from oven and set on wire rack. Poke holes in cake with skewer at 1/2" intervals while still hot and in pan.
Pour soaking mixture over cake- if it pools, make additional holes. Allow to set 30-40 minutes then flip cake upside down onto serving platter; remove pan.
Cool completely. Drizzle with glaze. Cover with plastic wrap.
GLAZE: combine 1/2 cup powdered sugar and 1 T cold milk. Whisk til combined.