Prep chicken: Whisk the flour and all chicken seasoning together in a shallow dish. Dredge each breast in the mixture, shake off any excess, then transfer to a dry surface.
Cook chicken: Melt the 2 tablespoons butter in 2 tablespoons olive oil in a large, oven-proof skillet over medium-high heat. Once hot, add chicken and cook for 3-4 minutes or until golden (it will finish cooking in the oven). Transfer chicken to a plate and tent with foil, don't wipe out skillet. Caramelize onions: Melt 4 tablespoons butter and 1 tablespoon olive oil in the chicken drippings over medium heat. Add the onions, 1/8 teaspoon salt and 1/8 teaspoon pepper. Cook, stirring occasionally, until onions are caramelized and deep golden brown, about 20-25 minutes. Turn down the heat and/or add additional butter/olive oil if the onions start to scorch.
Preheat oven: The last 10 minutes or so of cooking the onions, preheat the oven to 400 degrees F.
Make sauce: Once the onions are caramelized, add the garlic, red pepper flakes, soy sauce and Worcestershire sauce and cook for 30 seconds. Add the flour and cook for one minute. Add the beef broth, beef bouillon and all sauce seasonings. Bring to a simmer until thickened. Taste and season with salt and pepper if desired (I don't add any.)
Add cheese: Once the sauce thickened, add the chicken back to the skillet; spoon some sauce over the chicken. Top each piece of chicken with one slice of provolone cheese followed by shredded Gruyere and Parmesan. Bake: Transfer the oven-safe skillet to preheated oven and bake at 400 degrees F for 10-15 minutes, or until the cheese is melted and chicken is cooked through. To serve, spoon more sauce over the chicken. This dish is fabulous served with mashed potatoes.