Combine kosher salt, garlic, pepper, and paprika into a small bowl.
Rinse out cavity and pat dry chicken with paper towels.
Transfer the sliced onion on a baking sheet and spread it out to accommodate the size of the bird. The chicken will be resting on the onions to absorb flavor, but you also want to roast/blacken the onions to get unbelievable flavorful crunchy onions.
Sprinkle the cavity with a few good pinches of seasoning.
Lay the chicken on top of the onions back facing up.
Drizzle the chicken and onions with olive oil. Rub the chicken all around back with oil.
Sprinkle the chicken with 1/2 of the remaining seasoning.
Flip chicken breast side up.
Drizzle the top of the chicken with more olive oil and rub it in. Get into the crevices.
Sprinkle the chicken with remaining seasoning.
Place in a preheated 300° oven for 3 hours. Temperature should read 165° when inserted on thickest part of thigh without touching bone. The time can be checked after 3 hours.
Remove the chicken. Use a spoon to scoop up the juices and drizzle it over the chicken.
Rest ten minutes before carving. You probably won't need a knife. It falls off the bone. Serve with the onions. Unbelievable!
*I have tested and roasted a 3 1/2 - 4 1/2 pound chicken using the following temperatures and times:250° for 5 hours275° for 4 hours300° for 3 hoursHow much time you choose to roast is up to you. For me, it depends on how much time I have that day. You can't go wrong with slow roasting.