Preheat the oven to 250 degrees F. Line 2 baking sheets with parchment.
In a large bowl, mix together the rice, corn and wheat cereal squares, cheese crackers, pretzel sticks and pepperoni slices.
Melt the butter a small pot over medium heat. Whisk in the tomato paste, Worcestershire, garlic salt, oregano, garlic powder and onion powder. Pour the mixture into the bowl with the dry ingredients and gently stir until everything is coated. Spread the mixture evenly on the prepared baking sheets.
Bake for 1 hour, stirring every 15 minutes (the pepperoni will get slightly crunchy). Let cool, then pour into a serving bowl and gently toss with the Parmesan. Serve at room temperature.