Prepare popcorn according to package directions. Remove all unpopped kernels. Combine popped corn and pepperoni stick, if desired, in 2-gallon resealable bag.
Drizzle melted Fleischmann's over popcorn mixture; seal bag and toss to coat. Combine spaghetti sauce mix and Parmesan; sprinkle over popcorn. Seal bag and toss to coat again. Spread popcorn mixture on 15x10-inch jelly roll pan.
Bake 5 minutes; stirring once. Store leftovers in airtight container.