The Kof-K says the tray doesn't need to be toveled if it doesn't touch the food.
Microwave Oven Tray- A glass microwave oven tray does not require tevilah if no food
actually touches the glass. If food is placed directly on the glass piece then the tray
should be toveled with a beracha.
This part is speculation: The Star-K psak to tovel without a ...