Heat oven to 400°F. Melt 1/4 cup butter in large saucepan over medium heat. Add 1/3 cup flour, salt and pepper; blend until smooth. Stir in half-and-half. Cook until mixture boils and thickens, stirring constantly. Stir in chicken and vegetables; cook until thoroughly heated. Pour filling into ungreased 2-quart casserole.
In small bowl, combine all topping ingredients; with fork or pastry blender mix until crumbly. Sprinkle topping over chicken mixture.
Bake at 400°F. for 20 to 30 minutes or until topping is golden brown and filling is bubbly.