If steak is not already thinly sliced, place partially frozen steak on a cutting board and slice across the grain about 1/8-inch thick. Season the sliced steak lightly with 1/2 teaspoon kosher salt and 1/4 teaspoon black pepper. Have sliced onion, red and green bell peppers, minced garlic, and Worcestershire sauce ready.

Cook onions and peppers

Heat a large, heavy skillet or cast-iron pan over medium-high heat. Add 1 tablespoon vegetable oil and 1 tablespoon butter. Once butter foams, add the sliced onions and bell peppers in an even layer. Season with 1/2 teaspoon kosher salt and the remaining 1/4 teaspoon black pepper. Sauté, stirring occasionally, until vegetables are soft and starting to brown, about 6–8 minutes. Add minced garlic during the last 60 seconds and stir to combine. Transfer the vegetables to a bowl and keep warm.

Sear the steak

Return the skillet to high heat. Add a drizzle of oil if pan looks dry. Add the thinly sliced steak in an even layer (cook in batches if necessary to avoid steaming). Let the steak sear undisturbed for 30–45 seconds, then toss and spread again. Cook until just browned but still juicy, about 1–2 minutes total. Add 1 teaspoon Worcestershire sauce, toss to combine, and remove from heat.

Combine steak and vegetables

Return the sautéed onions and peppers to the skillet with the steak. Stir to combine and warm together over low heat for 30–60 seconds. Taste and adjust seasoning with a pinch of salt or pepper if needed.

Cheese & Assembly

Prepare rolls: split the 8-inch Amoroso-style rolls lengthwise without cutting fully through, leaving a hinge. Butter the cut sides lightly with the reserved 1 tablespoon butter.

Toast rolls: Place a clean skillet or griddle over medium heat and toast the buttered cut sides of the rolls until golden, about 1–2 minutes. Remove and set aside.

Melt cheese over steak: With the steak-and-veg mixture still warm in the skillet, reduce heat to low. Arrange 2 slices of American cheese over half of the mixture (enough for one roll) and let the cheese melt for about 30–45 seconds; use a spatula to fold melted cheese into the meat. Repeat for the second portion and second roll.

Assemble sandwiches: Open each toasted roll, spoon an even portion of the cheesy steak, peppers, and onions into each roll. Close the roll and, if desired, press gently on the sandwich for a few seconds to help cheese adhere. Slice each sandwich in half if serving two people and serve immediately.

Optional Miso-Herb Roasted Mushrooms

If adding mushrooms (+$2 option), preheat oven to 425°F (220°C). In a small bowl, whisk together 1 teaspoon olive oil, 1 teaspoon white miso paste, chopped thyme, and 1/4 teaspoon black pepper until smooth. Toss the halved or sliced mushrooms with the miso mixture until evenly coated. Spread mushrooms in a single layer on a small baking sheet and roast 10–12 minutes, stirring once, until browned and tender.

Add to sandwich: After roasting, fold the mushrooms into the steak and vegetable mixture before applying the American cheese, or spoon roasted mushrooms on top of the assembled sandwich just before serving.