Preheat the oven to 350 degrees F (175 degrees C).

Melt butter in a 9-inch baking pan in the preheating oven. Remove pan.

Sprinkle brown sugar evenly over butter in the pan.

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, oil, vanilla, and egg together in a large bowl on low speed for 30 seconds, scraping the 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.