I figured it out!
The thing that turns inside my microwave is just a little gear that a plate sits on with wheels. I can remove the wheels and plate, but the gear still turns.
So I remembered I had a MicroWare pan (like a square jelly roll pan) that I had bought and it didn't fit inside my little microwave. So I removed the plate and wheel from the microwave, inverted the pan on top of the gear that turns and it forms a perfectly flat surface that doesn't move for my bacon cooking platter!
I really love the cookware. It can go in the oven too and it's very strong.