Preheat the oven to 325°F (163°C). Line a rimmed baking sheet with enough parchment paper or aluminum foil to hang over the sides of the sheet.
In a small bowl, mix together the salt, chili powder, cumin, allspice, cayenne, cinnamon, and paprika.
In a large skillet over medium-high heat, melt the butter. As soon as the butter melts, add the sugar and soy sauce. Stir until the sugar dissolves. Then stir in the spices until combined.
Add the pecans and toss to coat them in the spiced butter. Cook, tossing and stirring frequently, until the butter is absorbed by the pecans, 2 to 3 minutes.
Spread the pecans on the baking sheet and roast until fragrant and toasted and the coating is caramelized, 13 to 15 minutes. (If the pecans are mired in a puddle of sugary spiced butter, that's fine. You can break them apart later when they're not hot.)
Let the spiced pecans cool on the baking sheet for about 10 to 15 minutes. Taste and, if desired, add a pinch of salt. Serve while still warm. (And when we say warm, we mean the pecans truly are best when warm—so good, in fact, we doubt there'll be any that have a chance to cool to room temperature.)