Slice mushrooms and fry in butter at medium high heat until browned slightly. Try not to stir often so they brown faster and not just turn watery. Set aside on plate when done.
Fry bacon until crispy. Remove from pan and chop into peices. Remove all but 2 tbs of the bacon grease. This is needed for next step.
Add the onion to the frying pan with the remaining bacon grease left in the pan. Saute onions over medium heat until tender.
Add the mushrooms, bacon peices, and fresh spinach to the onions and continue to cook until the spinach is wilted. Remove from heat and set aside.
Pound the chicken breasts flat with the smooth side if meat mallet. Lay out plastic wrap on counter and lay flattened breast on wrap so it forms a rectangular shape with the breasts edges overlapping so it looks like picture below. Season with the salt and pepper.
Layer the chicken with the ham then the swiss cheese on the chicken.
Spread the mixture from the frying pan thinly over the swiss cheese.
Roll the chicken up jelly roll style. Wrap tightly in plastic wrap. Refrigerate for 2 hours.
Set up a dredging station with flour, then eggs, and thirdly the bread crumbs. I used cookie sheets. Then using wooden skewers, insert several where the overlap is so the chicken doesn't separate while cooking.
Bake on a wire rack at 375 until internal temperature reaches 165. Cooking time is approximately 70 to 80 minutes.
Melt the butter in a heavy-bottomed saucepan. Stir in the flour and cook, stirring constantly, until the paste cooks and bubbles a bit, but don't let it brown about 2 minutes. Add the milk and dijon mustard, continuing to stir as the sauce thickens. Bring it to a boil. Add salt and pepper to taste, lower the heat, and cook, stirring for 2 to 3 minutes more. Add cheddar cheese and stir until cheese is melted. Remove from the heat.
Slice chicken roll and top with cheddar cheese sauce.
