Prepare the sirloin steak by slightly tenderizing and flattening it thinner with a meat mallet. Generously season the sirloin with salt and pepper. Slice the steak thin and set it aside to marinate in the seasoning while you cook the peppers.
In a large skillet over medium heat, heat 1 tablespoon avocado oil. Add onion and bell peppers and season with salt, and pepper. Cook, stirring often, until vegetables are tender, approximately 10 minutes. Remove peppers and onions from skillet and set aside. Heat the remaining oil in skillet.
Add steak in a single layer. Cook the steak approximately 4 minutes stirring and flipping the meat often to ensure all sides are seared.
Return the onions and peppers to the skillet, season with oregano and mix well. Top with 5 slices of provolone cheese. Cover the skillet and cook approximately 2 minutes or until the cheese is melted.