1. In a small bowl, combine chili powder, cumin, paprika, red pepper, salt, pepper and brown sugar. Stir in oil; mixture will be moistened but crumbly.
2. Generously rub chicken on all sides with chili mixture. Let stand at room temperature for 30 minutes to marinate (or cover and refrigerate for up to 1 day).
3. Preheat gas grill to medium, or preheat broiler to high and set rack 6 to 8 inches from source of heat. Grill or broil chicken until firm, about 5 minutes per side. Let cool for 5 minutes, then cut into thin strips.
4. Warm tortillas as package label directs. Serve chicken with tortillas.