Combine onion powder, salt, smoked paprika, cumin, cayenne pepper, garlic powder, oregano, thyme, and brown sugar in a small resealable plastic bag and shake the bag to mix the spices. Pour spice mix into a small bowl.
Make 2 cuts in the chicken skin, on front and back of chicken; insert your hand underneath the skin in front and back and loosen and separate skin without tearing it. Rub the chicken skin and cavity with vegetable oil, and rub the spice rub over the chicken skin, inside the cavity, and beneath the loosened skin.
Preheat grill for medium heat.
Place the beer can on the preheated grill and sit the chicken onto the beer can. Grill until chicken is thoroughly browned, the juices run clear, and an instant-read meat thermometer inserted into the breast, not touching bone, reads at least 165 degrees F (75 degrees C), 1 to 1 1/2 hours.