1Cut each bread slice diagonally into 4 triangles. In ungreased 13x9-inch pan, arrange half of bread triangles. Top with thawed vegetables. Sprinkle with 2 cups of the cheese. Top with remaining bread.
2In large bowl, beat remaining ingredients with wire whisk until blended; pour over bread. Cover tightly with foil; refrigerate at least 2 hours but no longer than 24 hours.
3Heat oven to 325ºF. Bake covered 30 minutes. Uncover; bake about 40 minutes or until knife inserted in center comes out clean. Top with remaining 1/2 cup cheese; bake 5 minutes longer or until cheese is melted. Let stand 10 minutes before cutting.