Fill the mugs: Spray the insides of two 12-ounce mugs (1 1/2 cups capacity) with cooking spray. In a medium bowl, add pineapple and juice along with the brown sugar. Stir until brown sugar is dissolved as much as possible. Divide in half and pour into mugs.
Top the mugs: Wipe out the same medium bowl with a paper towel (less dishes!) and add egg, oil, baking powder, pumpkin pie spice, sugar, flour and milk, in that order. Whisk between each addition to combine. Pour half into each mug.