Season steak on both sides with salt, pepper and garlic powder.
Heat 1 tablespoon of the butter in a skillet on medium-high heat. Once hot, add the steak and cook on both sides 1-2 minutes. Don’t overcrowd the pan. Cook in 2 batches if necessary. Remove from the skillet and set aside.
Add the remaining butter to the skillet. Once melted, add the bell pepper, onion, mushrooms and garlic. Cook 3-5 minutes or until the vegetables are tender.
To the skillet, add Worcestershire sauce and beef broth. Turn the heat to high, and once the mixture comes to a boil, add the spaghetti. Stir frequently and cook until the pasta is al dente.
Add both cheeses, stir, and once melted, turn off the heat and fold in the reserved steak.