Mix together the salt, garlic powder, onion powder, and pepper in a small bowl.
Spray your slow cooker with cooking spray. Combine the veggies in the base of your slow cooker and sprinkle with 1/2 a TBSP of the mixed spices. Add 3 of the garlic cloves, minced.
In a small bowl, combine the room temperature butter, the remainder of the spices, and the remaining 3 cloves of minced garlic.
Spread the butter mixture underneath the chicken's skin.
Place the prepared chicken over the vegetables and sprinkle with freshly ground black pepper. Cover and cook on low for 4 to 6 hours or until an insta read thermometer registers 165 degrees and the juices don't run pink.
Prepare a baking sheet with tin foil, and turn your broiler on low. Put the chicken on the baking sheet and broil until the skin browns, watching carefully, about 5 to 10 minutes. Remove the chicken, tent it with tin foil, and allow to rest for 10 minutes before slicing and serving.
If your chicken is done closer to four hours, the vegetables might not be done yet. When you remove the chicken from the slow cooker, turn it up to high, cover it and continue cooking the veggies until the chicken is done broiling and resting.