Place the chicken breasts between two pieces of plastic wrap or in a large zip-top bag. Using a meat mallet or the bottom of a heavy skillet, pound each breast to an even thickness of about 1/2 inch (helps them cook evenly). Pat dry with paper towels.

In a small bowl, mix olive oil, garlic powder, onion powder, smoked paprika, salt and black pepper to make a paste. Rub the mixture evenly over both sides of the chicken breasts.

Heat a large skillet (preferably cast iron or heavy-bottomed) over medium-high heat until hot. Add a thin film of oil if skillet is dry. Add the seasoned breasts and sear 4–5 minutes on the first side without moving them, until a golden-brown crust forms.

Flip the breasts and cook another 4–5 minutes until the internal temperature reaches 160–165°F (71–74°C) and juices run clear. Remove the chicken to a plate and tent loosely with foil while you prepare the topping.

For the Philly-style topping

In the same skillet used for the chicken (add a little more butter or oil if the pan is dry), reduce heat to medium and add 1 tablespoon unsalted butter. Once melted, add the sliced onion (cut into thin half-moons) and sliced green bell pepper (thin strips).

Sauté vegetables, stirring occasionally, 6–8 minutes until softened and beginning to caramelize. If using mushrooms, add sliced mushrooms after 3 minutes and continue to cook until they release moisture and brown, about 4–5 more minutes.

Add minced garlic and Worcestershire sauce, stir for 30–45 seconds until fragrant. Season with the 1 teaspoon salt and 1/2 teaspoon black pepper and taste; adjust seasoning as desired.

Return the cooked chicken breasts to the skillet, nestling them into the vegetables. Spoon some of the vegetables on top of each breast so the flavors mingle.

For finishing

Reduce heat to low. Lay two slices of provolone cheese over each breast (or enough to cover). Cover the skillet with a lid for 1–2 minutes to melt the cheese. Alternatively, transfer breasts to a baking sheet and broil on high for 1–2 minutes until cheese is melted and slightly bubbly—watch closely to prevent burning.

If serving as a sandwich: split and toast the hoagie rolls, spread mayonnaise on the cut sides, then place a chicken breast with melted provolone and pile the onion/pepper mixture on top. Sprinkle with chopped parsley if using.

If serving plated: transfer the chicken breasts to plates, spoon remaining vegetables over and around each breast, and garnish with parsley.

Serve immediately.