Preheat the oven to 400 degrees. Cook the sausage on a baking sheet to an internal temperature of 155 degrees using a thermometer. Once cooked set aside to rest.
Season the chicken on both sides with salt and pepper.
Heat a nonstick pan on medium heat. Once hot, add the oil. Saute the garlic and onion until soft. Add in the chicken and nicely brown on all sides.
Slice the sausage about 1/2 inch thick and add it into the pan.
Add in the pepperoncini, fresno peppers (if using), broth, thyme, and lemon juice; bring to a low simmer, adjust the heat accordingly. Let simmer for 10 to 15 minutes to build flavor.
Season the sauce with salt and pepper to taste. Add in the butter. Slowly stir in the cornstarch mixture a little at a time to a creamy consistency. (If the sauce is too thick, thin it out with a little more broth, if too thin, add a little more cornstarch/water mixture)
Serve with bread. Garnish with thyme.
Notes
Pro tips: Butterfly the chicken: Lay the breasts down on a cutting board, using a sharp knife parallel to the cutting board slice the breasts through the middle (carefully) all the way in half.