Step 1

Heat oven to 350°F. Spray 13x9 (3-quart) baking dish with cooking spray. Cook rice as directed on package; set aside.

Step 2

Meanwhile, in 10-inch nonstick skillet, melt 2 tablespoons butter over medium-high heat. Add onion, mushrooms, thyme, salt and pepper; cook and stir 4 to 5 minutes or until tender. Stir in flour until well combined. Slowly add milk, and heat to simmering, stirring to prevent lumps. Add chicken broth, Worcestershire sauce, sour cream, cream cheese spread and poppy seed; simmer 3 to 5 minutes, stirring frequently, until slightly thickened.

Step 3

In large bowl, mix chicken, cooked rice and sauce mixture; transfer to baking dish. Bake 25 to 30 minutes or until 165°F in center. Meanwhile, in large resealable food-storage plastic bag, mix crackers and 2 tablespoons melted butter, shaking to combine. Sprinkle on top of casserole during last 5 minutes of baking.

Step 4

If making ahead to bake and serve at a later date: Line 13x9-inch (3-quart) baking dish with 2 layers of plastic wrap, leaving enough overhang to completely enclose assembled casserole. Spread rice mixture in large shallow pan; cool mixture completely, covered, 30 to 45 minutes in refrigerator. Spoon rice mixture into baking dish; cover with another layer of plastic wrap. Freeze unbaked casserole about 8 hours or until completely frozen. Transfer frozen casserole to labeled 2-gallon resealable freezer plastic bag. Remove air; seal and freeze up to three months. To bake: Spray 13x9-inch (3-quart) baking dish with cooking spray. Remove plastic wrap from casserole; place in baking dish. Cover tightly with foil; thaw completely in refrigerator, 24 to 48 hours. Heat oven to 350°F. Uncover; bake 50 minutes. Sprinkle cracker mixture on top of casserole; bake 5 to 10 minutes longer or until crackers are golden brown and casserole is heated through (165°F in center).