Preheat the oven to 325°F and line a cookie sheet with a silicone mat or parchment paper. In a small saucepan, combine the water, brown sugar, salt, pepper, and chili powder. Cook over low heat for 5 to 8 minutes, stirring until the sugar is completely dissolved. Add the pistachios, pecans, and almonds and stir well to coat. Pour the nut mixture onto the prepared cookie sheet.

Bake for 10 minutes, then stir and continue baking for another 10 to 12 minutes until the coating is set. Remove from the oven and allow the nuts to cool completely. As they cool, the coating will harden and the mixture will break into pieces. Transfer to a bowl and set aside.

Reduce the oven temperature to 250°F. In a large mixing bowl, combine the Corn Chex, Rice Chex, pretzels, and Goldfish crackers. Pour the melted butter and Worcestershire sauce over the mixture and toss gently until everything is coated.

Sprinkle in half of the garlic powder, onion powder, and ground mustard and toss gently to combine. Add the remaining half of the spices and toss again. Spreading the seasoning in two stages helps it distribute more evenly and prevents clumping.

Spread the seasoned cereal mixture onto the cookie sheet and scatter the cooled candied nuts on top. Stir gently to combine. Bake at 250°F for 65 to 70 minutes, stirring and rotating the pan every 15 minutes to ensure even drying and crunch.

Remove the mix from the oven and allow it to cool for 5 minutes. Sprinkle the fresh-grated Parmigiano evenly over the mix, stir gently, and allow everything to cool completely before storing. Adding the cheese after baking prevents it from burning and ensures it sticks lightly to the warm mix.