1Heat oven to 375°F. Cook and drain pasta as directed on package; set aside.
2In 3-quart saucepan, melt butter over medium heat. Add onion, mustard, salt, pepper and garlic; cook 5 to 7 minutes, stirring occasionally, until onion is tender. Stir in flour. Cook over medium-low heat, stirring constantly, until mixture is bubbly. Remove from heat.
3Stir in yogurt, stirring constantly. Gently stir in cheeses; stir in pasta. Pour into ungreased 2-quart casserole. Sprinkle with bread crumbs.
4Bake uncovered about 25 minutes or until bubbly.