Place the Chex cereal, Goldfish, pretzels, and Cheez-its into a large mixing bowl.
In a separate small bowl, blend the melted butter, Worcestershire, seasoned salt, garlic powder, and onion powder with a whisk.
Drizzle the butter mixture over the dry ingredients and toss gently to coat. Then dust with Parmesan and mix once more.
Distribute the mixture in a thin layer across a large sheet pan or divide between two smaller ones. Frequent stirring means an even layer isn't essential.
Heat in an oven set to 250°F (120°C) for 45 to 50 minutes, stirring every 15 minutes, until crisp and lightly browned.
Let the snack mix cool fully on the pan, then either serve right away or keep in an airtight container for up to 2 weeks.