Savory Green Bean & Mushroom Casserole

WHAT YOU'LL NEED

• 4 Tbsp. I Can't Believe It's Not Butter!® Spread, divided
• 1 package (10 oz.) mushrooms, sliced
• 1/2 cup finely chopped sweet onion
• 1 Tbsp. all-purpose flour
• 1 1/2 cups water
• 1/4 cup heavy cream
• 1 tub Knorr® Homestyle Stock - Chicken
• 1 tsp. fresh thyme
• 1/8 tsp. ground black pepper
• 2 lbs. green beans, trimmed, cut into 2-inch pieces and blanched
• 1/4 cup plain dry bread crumbs