Season chicken breasts on both sides with salt and pepper. With "pretty" side up, take a spatula and paint on an even layer of dijon mustard onto each chicken breast.
On a plate or shallow bowl, pour pecan bits into an even layer. Place the chicken dijon-side down into the nuts and press gently so they adhere.
Lay chicken with nutty-side up on a cooking sheet lined with foil and greased with cooking spray. Place into oven and bake for 22 minutes, then remove and let cool for at least 5 before slicing!