Preheat oven to 350°F and spray your cake pans with nonstick spray.

Whisk together all the dry ingredients in a large bowl.  Make a well in the center. 

Combine the melted coconut oil, sugar, eggs, buttermilk, and vanilla in a medium bowl, and whisk until smooth.  Add to the flour mixture and fold in until almost incorporated.  Then fold in the banana, pineapple (with juice), and pecans until combined.

Divide the batter evenly between your cake pans and smooth with an offset spatula (I like to give it a little dip in the middle to combat a domed top).  Tap the pans sharply to reduce air bubbles.

Bake for 25 to 35 minutes, until a toothpick inserted in the center comes out clean and the edges are pulling slightly away from the pan.  Let the cakes cool in the pans for 15 minutes before inverting onto wire racks to cool completely.

To make the frosting, add the butter and cream cheese to the bowl of your mixer and beat on high speed until it begins to thicken and fluff.  Make sure your ingredients are *too* warm or soft, or it will just be greasy.  

Slow down the mixer and carefully add in the powdered sugar a cup at a time, beating slowly to incorporate.  Once all sugar has incorporated, turn mixer back to high to continue whipping.  Add in the pineapple juice and vanilla and continue whipping until it is smooth and fluffy. 

Frost right away or put the frosting in the refrigerator until you're ready to use.