Preheat oven to 350 degrees F (175 degrees C).
Lightly grease a 9x13 inch baking dish.
In a shallow dish or bowl, combine the bread crumbs, cheese, onions, and mustard powder; set aside.
Melt butter in a small saucepan; add garlic and Worcestershire sauce, and saute garlic until tender.
Remove from heat.
Dip chicken breasts in garlic butter mixture, then roll in bread crumb and cheese mixture, coating thoroughly.
Place coated chicken in the prepared baking dish.
Drizzle with any remaining garlic butter mixture.
Bake in the preheated oven for 30 to 40 minutes, or until chicken is no longer pink and juices run clear.