Add butter to the skillet and allow it to melt.

Add thin-sliced steak to the skillet in an even layer.

Season the steak with salt and black pepper.

Cook the steak for 3 to 4 minutes, stirring occasionally, until browned and cooked through.

Continue cooking until most of the moisture has evaporated from the skillet.

Remove the cooked steak from the skillet and set it aside on a plate.

Keep the skillet over medium-high heat.

Add sliced onions and sliced bell peppers to the skillet.

Cook the onions and peppers for 4 to 5 minutes, stirring occasionally, until they soften and any released liquid cooks off.

Return the cooked steak to the skillet and stir to combine with the onions and peppers.

Reduce the heat to low.

Lay provolone slices on top of the steak and vegetable mixture in the skillet.

Cover the skillet with a lid and cook for 1 to 2 minutes until the cheese melts.

Remove the skillet from the heat.

Place romaine lettuce leaves on serving plates.

Spoon the hot steak, onion, and pepper mixture with melted cheese into each lettuce leaf to form boats.

Serve immediately.