Melt margarine in glass square pan 9x9x2 in microwave. Sprinkle brown sugar over margarine. Arrange pineapple slices in pan and place cherry in center.
Beat sugar, shortening, egg and milk for 30 seconds. Add flour, baking powder, and salt. Mix well scraping bowl often. Beat on high speed for 3 minutes, scraping bowl occasionally. Pour over fruit in pan.
Microwave pan 6-8 minutes, or until it pulls away from sides of pan. Immediately invert onto a heatproof plate. Let glass pan remain over cake a few minutes and serve.