In a large saucepan, melt 2 tablespoons butter. Stir in the flour, Italian seasoning, garlic powder and pepper until blended. Gradually add milk. Bring to a boil; cook and stir for 1-2 minutes or until thickened. Reduce heat to low; stir in the cheeses until smooth (sauce will be thick). Fold in the broccoli and mushrooms.
Spoon into a greased shallow 2-qt. baking dish. Melt remaining butter; toss with bread crumbs. Sprinkle over vegetable mixture. Bake, uncovered, at 350° for 30-35 minutes or until golden brown.