Stir together 2 tablespoons of olive oil, cayenne pepper, black pepper, ground paprika, salt, mustard powder, and garlic powder in a small bowl to make a paste.
Prick steaks all over with a fork and rub them well with the spice rub paste, working the rub into the meat.
Heat a large, heavy skillet over high heat and add the remaining 3 tablespoons of olive oil. Heat oil until it just begins to smoke and quickly sear the steaks until the outside has browned but the center is still blood red and just warmed, 2-3 minutes per side. An instant-read thermometer inserted into the center should read 115 degrees F (46 degrees C).
Remove steaks from skillet with tongs. Pour the dry red wine into the skillet, and bring to a boil while scraping the browned bits of food off of the bottom of the pan with a wooden spoon. Stir in the sliced portobello mushrooms, and cook and stir until mushrooms are cooked and have released their liquid, about 5 minutes.
Return steaks to the skillet on top of the mushroom-wine sauce. Reduce heat to LOW and cook until sauce reduces and thickens, about 5 minutes. Remove steaks to serving platter and pour mushroom sauce over steaks to serve.
