Combine onion, garlic, cumin and a little stock in a large pan. Cook until onion and garlic are soft. Add rice, stir well.
Add a cup of stock at a time, stirring constantly until rice is cooked and creamy. This will take about 15 - 20 minutes. Halfway through cooking, add the spinach.
Fold in cooked chicken. Cook until heated through. Serve in bowls, sprinkled with Parmesan cheese.