Melt butter in a 9-inch baking pan in the preheating oven. Remove pan.
Sprinkle brown sugar evenly over butter.
Arrange pineapple chunks in a single layer over the butter and brown sugar, then sprinkle with pecans; set aside.
Beat biscuit baking mix, white sugar, milk, vegetable oil, vanilla extract, and egg together in a large bowl on low speed for 30 seconds, scraping bowl constantly.
Increase mixer speed to medium and continue beating until batter is smooth, about 4 minutes more.
Slowly pour batter over the pineapple mixture.
Bake in the preheated oven until a toothpick inserted into the center comes out clean, 30 to 35 minutes.
Run a paring knife between the cake and the edge of the pan to loosen cake. Cover the cake pan with a plate, and invert it to flip the cake out of the pan and onto the plate. Cool at least 10 minutes before serving.
