In large saucepan, stir together the rice and broth; bring to boil, reduce heat to low, cover and simmer until rice is tender.
In another large skillet, add the butter and mushrooms and cook over medium heat until mushrooms soften, then add the pepperoni slices and continue cooking until pepperoni crisps slightly; remove from heat.
Add the cooked rice to the skillet with mushrooms and pepperoni, stir to combine, and top with cheese.