Chop spinach and cheese and mix. This will be the stuffing.
Open the chicken breasts creating a cavity as in a bag and stuff with the spinach and cheese. Seal the hole with a toothpick or two.
Heat some oil in a pan and add the chicken breasts; cook slightly on both sides and add boiling chicken broth (enough for fully covering the chicken).
Add the mustard and the honey and let it cook for about 8 minutes.
The breasts will be done when transparent liquid comes out upong pricking. When ready, remove from the liquid and let it boil for another 10 minutes, creating a honey mustard sauce.