Preheat oven to 375 F. Spray an 8-inch baking dish with cooking spray; set aside.
Using a sharp knife, make a lengthwise cut in the thickest side of the chicken breasts, being careful not to cut all the way through.
Divide cheese & pear slices between the 4 chicken breasts to fill the pocket in each. Any remaining pear slices can be laid on the bottom of baking dish. Arrange stuffed chicken breasts over extra pear slices then top with gravy.
Bake 25-30 minutes or until chicken is cooked. Sprinkle with sage or thyme.