Set oven to 375°F. Lightly grease a 9x13-inch baking dish.
In the prepared dish, combine olive oil, chicken broth, heavy cream, paprika, garlic powder, ground mustard, peas and carrots, corn, and orzo. Add 1 cup Cheddar, ⅓ cup Parmesan, salt (I add 1 teaspoon), and pepper (I add 1 teaspoon). Stir gently until everything is well combined and press into an even layer.
Sprinkle ½ cup Cheddar and ⅓ cup Parmesan evenly over the top. Bake, uncovered, for 40-45 minutes, or until the orzo is tender and creamy.
Remove from the oven. Add diced chicken, broccoli, and remaining ½ cup Cheddar. Gently stir through then let the casserole rest, covered with foil, for 10 minutes to thicken.
Stir gently once more. Taste and adjust seasonings and serve warm.
