Lightly grease a 9x13 baking dish with cooking spray and set aside.
Add olive oil to a 12-inch skillet and set over medium-high heat. Add diced chicken to the pan; cook, stirring occasionally, for about 8 minutes, or until chicken is browned and cooked through. Transfer the chicken to a medium mixing bowl and set aside.
Add zucchini and bell peppers to the pan; cook, stirring occasionally, for about 4 minutes, or until the vegetables are just tender. Add garlic and cook for 20 seconds. Stir in corn and cook for 1 minute, or until heated through. Transfer the zucchini mixture to the bowl with the chicken. Set aside.
Add butter to the same pan and melt. Stir in flour; cook, stirring constantly, until the flour starts to brown, about 1 minute. Whisk in broth and half & half; bring to a boil, whisking often.
Remove from heat; stir in cream cheese and 3/4 cup mozzarella; continue to whisk and stir until melted. Season with salt and pepper.
Drain liquid from the chicken and vegetable mixture. Stir the chicken and vegetables into the cheese sauce. Transfer chicken and veggies to previously prepared baking dish.
Sprinkle the casserole with the remaining mozzarella cheese. Bake for 22 to 25 minutes, or until edges are bubbly and top is browned. Remove from oven and let stand 10 minutes.
Taste for salt and pepper; adjust accordingly.
Garnish with parsley and serve.
How to Know When the Casserole is Done: Oven cooking capability can vary from brand to brand, so you might need to adjust the cooking time, just slightly. If the edges of the casserole are bubbly and the top is a nice golden-brown, you're good to go.
Cut the Chicken into Same-Size Pieces: If there are some big cubes and some smaller ones, the chicken pieces could turn come out underdone or overdone. Keeping them the same size is a good way to ensure that all the chicken gets cooked through.
Use Leftover Chicken: If you have leftover cooked chicken from a previous dinner, feel free to use it in this recipe - it's a real time saver!
WW POINTS: Shave off 2 points by using Fat Free Half & Half, Reduced Fat Cream Cheese, and Reduced Fat Shredded Mozzarella.