Preheat The Oven & Prep Your Pan. Start by preheating the oven to 250 degrees F. Line a cookie sheet (13"x18," often called a half sheet pan) with parchment paper.

Combine The Dry Ingredients. In your largest large bowl, combine gluten-free pretzels, corn Chex, rice Chex, Cheerios, and Nuts. Stir to combine well, so everything is pretty evenly distributed.

Mix Up Your Seasoning Sauce. In a microwave-safe bowl, melt the butter in 15-second increments until fully melted and liquid. Stir in Worcestershire sauce, seasoned salt, garlic powder, and onion powder. Stir or whisk to combine until uniform and well blended.

Toss To Coat. Pour the seasoning sauce over the dry ingredients and stir to combine. Stir for at least a full minute, to really distribute the sauce well.

Spread Out. Turn the Chex mix mixture out onto your prepared pan and spread into an even layer.

Bake, Stir & Cool. Then, bake the Chex mix at 250 degrees F for one hour, stirring every 15 minutes for even browning. Allow the Chex mix to cool completely before storing (so that it's as dry as possible).

Serve Or Store. Then, dive in and serve immediately or place cooled Chex mix in an airtight container and store at room temperature up to 5 days.