Preheat oven to 350F (180C). Spray a 9- x 13-inch baking dish with cooking spray and set aside.
Melt butter in a large skillet over medium-high heat. Add flour and stir to cook for about 1 minute. Whisk in broth, milk, salt and thyme and bring to a simmer, stirring constantly. Allow sauce to cook until it thickens, whisking regularly so that the sauce is smooth (about 5-10 minutes).
Remove from heat, stir in cooked pasta, ½ cup of mozzarella, chicken, zucchini, and corn.
Transfer chicken mixture to prepared dish. Top with remaining mozzarella and sprinkle with Parmesan.
Bake, uncovered, until bubbly and heated through (about 20-25 minutes).
Notes
Always preheat the oven before baking the casserole for best results
Use high-quality chicken (free range is always best and makes a huge difference in flavor).
Fresh thyme will give a stronger flavor but you can use dried if you don't have it. See my recommendations below.
Whole wheat pasta is lower in calories and higher in fiber and nutrients than white pasta so if you want to make easy healthy meals it's a good alternative to white pasta.
Frozen corn can be used instead of fresh but when fresh corn is in season it's worth buying.
Use low-fat milk instead of full fat or cream. This will reduce fat and calories and is an easy way to make weeknight meals lighter.
No zucchini? Spinach or broccoli would be great substitutes. Try to stick with green veggies with a lot of nutrients