Preheat the oven to 425°F and line a large sheet pan with foil.
Pat the chicken thighs completely dry with paper towels; do not trim excess fat, which will render during cooking.
In a small bowl, whisk together the olive oil, balsamic vinegar, chili powder, cumin, garlic powder, and paprika until combined.
Season the mixture with salt and pepper to taste (about 2 teaspoons fine salt and 1½ teaspoons black pepper as a guide).
Brush or rub the seasoning mixture evenly over the back and then the front of each thigh so all thighs are coated and the mixture is used up.
Arrange the thighs skin-side (if any skin) up or flat on the prepared sheet pan, spacing them so they are not touching.
Bake on the center rack for 15 minutes.
Move the oven rack to about 8 inches from the heat source, switch to broil, and broil 7–10 minutes until the tops are nicely blackened and caramelized—watch closely to avoid burning.
Remove from the oven, tent loosely with foil, and let rest 5–10 minutes. Brush any pan juices over the thighs and slice or chop as desired before serving.
