Creamy Chicken and Broccoli Casserole

1 (12-ounce) package steam-in-bag broccoli florets
1 tablespoon canola oil
1 cup prechopped onion
2 (8-ounce) packages presliced mushrooms
3 tablespoons all-purpose flour
1 1/2 cups fat-free milk
12 ounces chopped skinless, boneless rotisserie chicken breast (about 3 cups)
1/2 cup plain fat-free Greek yogurt
1/4 cup canola mayonnaise
1/2 teaspoon freshly ground black pepper
1/4 teaspoon salt
2 ounces sharp cheddar cheese, shredded (about 1/2 cup)
1 ounce Parmesan cheese, grated (about 1/4 cup)

  1. Preheat broiler.

  2. Prepare broccoli in microwave according to package directions.

  3. Heat a large ovenproof skillet over medium-high heat. Add oil to pan; swirl to coat. Add onion and mushrooms; cook 12 minutes or until mushrooms brown and liquid evaporates, stirring occasionally. Sprinkle mushroom mixture with flour; cook 1 minute, stirring constantly. Stir in milk. Bring to a boil; cook 3 minutes or until thick and bubbly. Stir in broccoli and chicken; cook 1 minute. Remove pan from heat. Stir in yogurt, mayonnaise, pepper, and salt. Top evenly with cheeses; broil 2 minutes.