In a small bowl, combine onion powder, garlic powder, thyme, oregano, sage, black pepper, cayenne pepper, mustard powder, paprika, celery seeds, and salt. Mix well.
Rub your chicken breasts with olive oil, followed by the seasoning. Make sure the chicken breasts are well coated.
Fill your pellet grill with your preferred wood pellets and preheat it to 375℉. Place the chicken breasts on the grill and smoke for 20-30 minutes, flipping halfway.
Once the chicken breasts reach 165℉, remove them from the grill and let them rest for 5 minutes before serving.