Preheat the oven to 375 degrees.
In a skillet, melt the butter. Saute the diced onions & mushrooms for about 7 minutes or until lightly browned. Stir in the minced garlic & cook for an additional 1-2 minutes. Season with a little salt & pepper. Cook for 7-9 minutes, until the mushrooms have lightly browned and are tender.
Add in the cream cheese. Stir around until it’s melted & combined. Turn off the heat, & stir in the cheddar cheese & the bacon (if using).
Butterfly the chicken breasts. Season the inside with salt & pepper. Spread the cream cheese mixture over the butterflied chicken breasts. Roll the chicken breasts up tightly, like a burrito. Season the top with salt, pepper, & a little paprika.
Bake uncovered 375 degrees for 35-40 minutes, or until the juices run clear.