Instructions

• Preheat the oven to 200°F (95°C) to keep the cooked cutlets warm.
• Set up three shallow bowls: one with the 1/3 cup all-purpose flour, one with the lightly beaten large egg, and one with the 1/3 cup panko breadcrumbs.
• Lightly season both sides of the 2 thin cutlets (steak, veal, chicken, or turkey) with kosher salt and freshly ground black pepper from the amounts listed. Dredge each cutlet in the flour, shaking off excess; dip into the beaten egg; then coat evenly with the panko, shaking off excess. Do not press the breadcrumbs into the meat. Do not refrigerate the breaded cutlets; fry them immediately.
• Heat a frying pan or skillet over medium–medium-high heat and add a thin film of oil to coat the bottom of the pan. When the oil is hot, add the breaded cutlets and fry until lightly browned—briefly on each side (time will depend on thickness). Transfer the cooked cutlets to a plate and keep them warm in the preheated oven; do not tent with aluminum foil.
• If there is an excess of oil in the pan, pour off enough so there is only a thin film left (leave any browned bits). Return the pan to medium heat.
• Add the halved, thinly sliced medium yellow onion to the pan and cook, stirring occasionally, until lightly browned, about 6–8 minutes.
• Add the thinly sliced 1/2 red, 1/2 green, and 1/2 yellow bell peppers, the 4 ounces thinly sliced mushrooms, 1/4 teaspoon garlic powder, 1/4 teaspoon onion powder, and the remaining kosher salt and black pepper from the amounts listed. Cook, stirring occasionally, until the peppers are crisp-tender, about 4–5 minutes.
• Push the cooked vegetable-and-mushroom mixture into two even piles in the pan. Place 2 slices of Provolone or Swiss cheese over each pile and let the cheese melt.
• Spread mayonnaise and grainy mustard on both cut sides of 2 of the lightly toasted crusty hoagie rolls (one roll per sandwich).
• Place one warm fried cutlet on each prepared roll, top each cutlet with one portion of the vegetable-and-cheese mixture, close the rolls, and serve immediately.