Mix the brown sugar, salt, chili powder, paprika, garlic powder, onion powder, oregano, and pepper in a medium bowl.
Pat the chicken thighs dry with a paper towel. Drizzle with olive oil.
Sprinkle the spice mixture generously all over each chicken thigh and gently rub it in until well coated.
Preheat the Blackstone to medium heat and oil as needed.
Place the seasoned thighs onto the Blackstone. Cook for 3-4 minutes.
Turn the thighs and cook for an additional 3-4 minutes. Adjust the heat as necessary. The thighs should be beginning to brown without getting overly dark.
Reduce the heat to medium-low. Brush both sides of the chicken thighs generously with barbecue sauce. Continue cooking on each side for 2-3 additional minutes. When done, the internal temperature should be 165°F in the thickest part of each thigh.
Let cool for 10 minutes before serving.