Preheat the oven to 350 degrees Fahrenheit. Grease a 9-inch square baking dish and set aside.
In a shallow bowl combine, ½ cup melted butter, 1 tablespoon Worcestershire sauce, 1 teaspoon ground mustard, ½ teaspoon garlic salt, and ¼ teaspoon pepper.
Place ½ cup crushed fried onions in another shallow bowl. Dredge 4 boneless skinless chicken breasts in the butter mixture and then coat in the bowl of crushed onions. Place each chicken breast in the prepared baking dish.
Sprinkle the remaining crushed onions on the top on top of the chicken then drizzle the remaining butter sauce on top.
Bake for about 30 minutes until no longer pink and cooked throughout.