Heat oven to 350F. Spray casserole pan with cooking spray; set aside.
On large cookie sheet, place bread slices, Bake for 15-20 minutes. Turning each side once, until firm and golden brown. Remove bread slices from cookie sheet; cut into 1/2 inch cubes.
In a large skillet, eat the oil over med- high heat Add celery, onion and carrots; cook 6 to 8 minutes, stirring frequently, until tender. Stir in broth, sage,thyme and pepper; heat to boiling. Remove from heat. Stir in the bread cubes until well blended. spoon mixture into casserole pan.
Cover; bake 30 minutes. Uncover; bake 15-20 minutes longer or until hot and top is light golden brown.