Preheat oven to 350°F. Mix bread crumbs, 2 tablespoons of the Parmesan cheese and 2 tablespoons of the butter, melted, in small bowl. Set aside.
Melt remaining 2 tablespoons butter in large skillet on medium heat. Add onion; cook and stir 5 minutes or until tender. Stir in flour, garlic salt, thyme and pepper. Add milk; cook and stir until thickened and bubbly. Add cream cheese and remaining 1/4 cup Parmesan cheese; cook and stir until cream cheese is melted. Add cooked green beans and tomatoes; toss gently to coat.
Spoon into 2-quart baking dish. Sprinkle top evenly with crumb mixture.
Bake 25 minutes or until heated through and top is lightly browned.