In a large pot, bring the water to a boil. Add the broccoli and cook for 5-7 minutes or until tender. Drain well and set aside.
Spray a large skillet with vegetable spray and saute the onion and garlic over medium heat until tender. Drain.
In a large saucepan, combine the yogurt and flour, stirring well with a wire whisk. Add the broth, water, salt and pepper. Cook over medium heat for 30 minutes or until thickened and bubbly, stirring often. Add the broccoli and onion mixtures and the shredded cheese, stirring until the cheese melts. Serve hot.