Step 1

Heat oven to 350° F. Spray 8-inch square baking dish with cooking spray.

Step 2

In 12-inch nonstick skillet, heat olive oil over medium heat. Add onion; cook 3 to 4 minutes, stirring frequently, until translucent. Add mushrooms and salt; continue to cook 4 to 6 minutes or until any liquid evaporates and mushrooms are brown. Add broccoli; cook 30 seconds to 1 minute or until bright green. Transfer mixture to large bowl.

Step 3

Add rice to bowl. Stir to combine. Stir in chicken.

Step 4

In 1-quart saucepan, melt butter over medium heat. Sprinkle flour over melted butter; add 1/4 teaspoon salt. Beat with whisk. Cook 1 to 2 minutes or until mixture turns light brown. Slowly beat in milk with whisk 2 tablespoons at a time until smooth and combined. Heat to boiling, stirring constantly. Continue to cook and stir 1 minute. Remove from heat; cool 5 minutes.

Step 5

Slowly beat sour cream and Cheddar cheese into sauce mixture with whisk. Reserve 2 tablespoons Parmesan cheese; set aside. Beat remaining Parmesan cheese into milk mixture. Add to bowl with chicken and vegetables; stir to combine. Pour into baking dish; spread evenly.

Step 6

Bake 20 to 25 minutes or until heated through. Top with remaining Parmesan cheese. Bake 5 minutes longer.