Rub chicken with 1/2 tablespoon oil and season with salt and pepper. Rub with 1 teaspoon Italian seasoning, 1/2 teaspoon garlic salt, and place on a sheet pan.
Add onions and peppers (and mushrooms if using) to a mixing bowl. Drizzle with 1 tablespoon oil, and season with 1 teaspoon Italian seasoning, 1/2 teaspoon garlic salt, and pepper. Spread out on baking sheet next to chicken.
Bake for 25 minutes until chicken is cooked to 165 degrees F internal temp and the veggies are tender. Remove from oven and turn the heat down to 350 degrees F.
Using two forks, shred chicken and mix together to spread seasoning.
Slice rolls in half to you have tops and bottoms. Place bottoms on a clean baking sheet. Layer chicken onto roll bottoms, top with veggies, and then with provolone slices.
Add bun tops and brush with melted butter. Sprinkle dried parsley and garlic salt over top of buns.
Bake for 12-15 minutes until cheese is melted and tops are golden. Remove from oven and cut apart into individual sliders before serving warm.