Preheat oven to 350 degrees F (175 degrees C). Line a baking sheet with aluminum foil and lightly coat with cooking spray.
Combine walnut halves, pecan halves, almonds, and cashews in a large bowl. Add salt, black pepper, cumin, and cayenne pepper; toss to coat.
Heat sugar, water, and butter in a small saucepan over medium heat until the butter is melted. Cook for 1 minute and remove from heat. Slowly pour butter mixture over the bowl of nuts and stir to coat.
Transfer nuts to the prepared baking sheet and spread into a single layer.
Bake nuts in the preheated oven for 10 minutes. Stir nuts until the warm syrup coats every nut. Spread into a single layer, return to the oven, and bake until nuts are sticky and roasted, about 6 minutes. Allow to cool before serving.
