Preheat oven to 375°.
Cut a 2-inch-long slit in side of meaty portion of each breast without cutting all the way through the breast. Slice cheese into 4 portions; brush with mustard. Place 1 cheese slice in each slit; secure with wooden picks.
Combine cereal and seasoning. Dip chicken in buttermilk; dredge in cereal mixture. Place chicken in a 13- x 9-inch baking dish coated with cooking spray. Bake at 375° for 1 hour. Remove picks, and serve immediately.
Tip: These stuffed bone-in chicken breasts are also tasty filled with Swiss cheese or provolone. Instead of the lemon-herb seasoning, you can use extra-spicy herb seasoning or Italian seasoning.