Confirm chicken is fully thawed and fits with the lid closed. Remove neck and giblets; pat chicken and cavity dry without rinsing.
Arrange four 1-inch onion rounds across the bottom of a 6-quart oval slow cooker. Add no broth or water.
Combine salt, paprika, garlic powder, onion powder, thyme, oregano and pepper. Rub chicken with oil and coat evenly with seasoning.
Set chicken breast-side up on onion rounds and tuck wing tips underneath. Cover immediately.
Cook on high 3 1/2 to 4 1/2 hours, beginning checks at 3 hours 15 minutes for a small bird or hot-running cooker.
Check both breasts and inner thighs without touching bone. Continue in 15-minute increments until every checked location reaches 165°F.
Transfer carefully with wide spatulas to a rimmed sheet pan. Rest 10 minutes before carving or optional broiling.
Brush skin lightly with oil and broil 6 to 8 inches from the element for 3 to 6 minutes, watching constantly. Rest 5 minutes, carve and serve.
