Mix the rub ingredients. Make sure it is fairly thick and sludgy. Add further oil if it is too thick.
Use an upside spoon to loosen the skin of the chicken. Spoon most of the rub ingredients under the skin and 1 tbsp of oil for the skin. Use a dessert spoon or hand to spread the paste inside the skin.
Insert the used lemon inside the chicken
Place the rack inside the slow cooker and chicken on top of the rack. Spread the remaining sludge, sprinkle salt and pepper.
Slow cook the chicken for 5 hours on low or 3 hours on high or until the juice started flowing or until the temperature reaches 75°C/165F on a meat thermometer.
Remove the cooked chicken from the slow cooker, sprinkle remaining oil on top. Broil or grill the chicken on medium-high for 5 to 10 minutes to get the crispy brownish golden texture.
Pour the pan juices on top and serve with lemon sauce.