Stir together the cumin, coriander, paprika, cinnamon, salt, pepper, and minced garlic in a small bowl. Rub this mixture evenly over all sides of the chicken thighs.
Place the sliced onion in the bottom of the slow cooker to create a base layer. Arrange the seasoned chicken thighs on top of the onion.
Scatter the zucchini rounds and green olives over the chicken. Pour the chicken broth evenly across the top.
Cover and cook on low for 6 hours. The chicken should reach an internal temperature of 165°F and the zucchini should be tender but still hold its shape.
Turn off the slow cooker and let the dish rest for 10 minutes before serving. Sprinkle the chopped parsley over the top.