Remove steak from the refrigerator, pat dry with paper towels, and let rest for 15 minutes. Meanwhile, heat a large cast iron skillet over high heat for about 5 minutes.
When skillet is hot, add a tablespoon of vegetable oil and swirl to coat the pan. Salt steak, add to pan, and cook for 3 to 4 minutes each side, or until a meat thermometer inserted into the steak reads 125°F to 130°F. Turn off heat, transfer steak to a cutting board, and cover loosely with foil.
Wipe out skillet and heat remaining vegetable oil over medium-high heat. Once shimmering, add onions and a pinch of salt and cook, stirring often, for 3 to 5 minutes. Add peppers and continue to cook, stirring, for 15 to 20 minutes, adjusting heat to medium if vegetables are browning too quickly. Stir in Worcestershire sauce and cook for another 2 to 3 minutes. Turn off heat, taste, and add salt and pepper as needed.
Slice steak as thinly as possible, then add the slices to the pan with the onions and peppers. Return heat to medium and stir to combine the steak and vegetables. Taste and adjust seasoning as needed.