– Preheat oven to 400 °F (205 °C).
– Skin chicken breasts, cut away filet mignon from the underside of chicken breast and draw out the tendons.
– In a blender, finely chop filets mignons of chicken with spinach. Add the egg and season with salt and pepper.
– Slit the breast top-center style, butterfly-style or tube-style, and fill the cavity with stuffing.
– Pour tomato sauce in a baking dish and add stuffed chicken breasts. Cover dish with aluminum foil.
– Cook in oven approximately 40 minutes.
– Carve stuffed chicken breasts into thin slices and arrange fan-like on a serving dish.