Spray a 9x13” baking dish with cooking spray and set aside.
Bring broth to a boil in a medium pot. Once boiling, add rice. Reduce heat to medium-low and simmer, covered, for 45 minutes. Meanwhile, cook broccoli according to package directions and set aside.
In a medium pan, heat one teaspoons olive oil over medium heat. Add onion and garlic and sauté under tender, about 5-6 minutes. Remove from pan and set aside.
In the same pan, add remaining teaspoons of olive oil and cook diced chicken breast over medium-high heat until cooked through. Season with ½ teaspoons of salt. Remove from pan and set aside with onion mixture.
To make the cheese sauce, whisk together ½ cup of milk and flour. Add to pan along with the other 1½ cups of milk. Whisk for about 5 minutes over medium heat, or until sauce has thickened. Remove from hear and add yogurt, 1 cup of cheese, remaining 1/2 teaspoons of salt and pepper to taste.
Pre-heat broiler. In a large bowl, stir together rice, broccoli, onion mixture, chicken and cheese sauce. Pour mixture in the greased baking dish. Top with remaining ½ cup of cheese and broil casserole until cheese is melted.