Preheat the oven to 350 degrees F (175 degrees C). Line a baking sheet with aluminum foil and lightly coat with cooking spray.
Combine walnuts, pecans, almonds, and cashews in a large bowl. Add salt, black pepper, cumin, and cayenne; toss to coat.
Heat sugar, water, and butter in a small saucepan over medium heat. Cook until butter is melted and sugar is dissolved, about 1 minute. Slowly pour butter mixture over 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 to coat with warm syrup; spread out in a single layer. Return to the oven and bake until nuts are sticky and roasted, about 6 more minutes. Allow to cool before serving.