Heat a large ovenproof skillet over medium heat and add the oil. Sauté the onion, garlic, and bell peppers until soft, about 5 minutes.
Combine the chili powder, paprika, cayenne, cumin, garlic powder, oregano, salt, and pepper in a dish, and use the mixture to season the flank steak with on both sides. Lay the steak flat on a cutting board with the grain running up and down. Place the sautéed onions and peppers in the middle of the steak, leaving an inch or so on both ends. Cover the onions and peppers with a layer of cheese.
Tightly roll up the meat from left to right; this will ensure that you cut against the grain when you slice the meat. Stick toothpicks through the sides of the roll to help it hold its shape and use a sharp knife to cut in between the toothpicks.
Return the skillet to high heat, add the steak, and sear until a nice crust has developed, about 3 minutes. Flip and repeat with the other side. Transfer the skillet to the oven and bake for 10 minutes, or until cooked to your preference.