Preheat the Blackstone grill over medium high heat (approximately 400 degrees F).
Add 1 tablespoon avocado oil and 1 tablespoon butter to the middle of the grill. Spread them around so the butter melts.
Add 1 sliced green bell pepper, 1 sliced red bell pepper, and 1 sliced white onion to the grill. Toss them to coat in the oil and butter, and sauté for 3 to 5 minutes until the peppers are cooked to your preference.
Move the peppers and onions to a cooler part of the grill (front or a part of the grill where the burner is off or remove from grill and set aside).
Place 4 hoagie rolls face down on the cooler side of the grill so they toast slightly. Watch them closely so the rolls do not burn.
Add 1.5 pounds chicken breasts that have been thinly sliced against the grain to the center of the grill and spread them into a thin layer. Season the chicken with 1 teaspoon Italian seasoning, 1/2 teaspoon salt, and 1/2 teaspoon pepper. Let the chicken sear for 3 to 5 minutes until the juices start to flow.
Flip the chicken and use your spatula to chop it into smaller pieces. Continue cooking for 2 to 3 more minutes until the chicken is cooked through.
Divide the chicken into 4 equal piles on the grill and top each pile with the pepper and onion mixture. Immediately top each pile with 2 slices provolone cheese and let the cheese melt for 1 to 2 minutes.
Use your spatula to scoop and lift each pile and place the mixture onto one of the toasted hoagie rolls.
Serve immediately while warm and enjoy!