Add the chicken pieces, rice, onion, garlic, chicken broth, salt, and pepper to the slow cooker. Stir to combine everything evenly.
Cover and cook on low for 4 hours or until the rice is tender and the chicken is cooked through.
Stir in 1 1/2 cups of the cheddar cheese until it melts into the mixture.
Add the broccoli florets and stir again. Cover and cook on low for 30 more minutes until the broccoli softens slightly.
Sprinkle the remaining 1/2 cup of cheese over the top. Cover for 5 minutes until the cheese melts before serving.