2 thin slices steak, veal, chicken, or turkey (, pounded to 1/4 inch thickness and to fit length of your bread roll)
1/3 cup all-purpose flour
1 large egg (, lightly beaten)
1/3 cup panko breadcrumbs
1 medium yellow onion (, halved and thinly sliced)
1/2 red bell pepper (, stems and seeds discarded, thinly sliced)
1/2 green bell pepper (, stems and seeds discarded, thinly sliced)
1/2 yellow bell pepper (, stems and seeds discarded, thinly sliced)
4 ounces button or cremini mushrooms (, thinly sliced)
1/4 teaspoon garlic powder
1/4 teaspoon onion powder
1/4 to 1/2 teaspoon kosher salt
1/4 teaspoon freshly ground black pepper
4 slices Provolone or Swiss cheese
Mayonnaise
Grainy mustard
4 crusty hoagie rolls (, lightly toasted)