Position a broiler rack 4 to 5 inches from the heat, and a second rack in the lower third of the oven. Preheat the broiler. In a large skillet, heat 1 tbsp. EVOO over medium-high heat. Add the onion and bell peppers; season with salt and pepper. Cook, stirring, until tender, about 4 minutes.
Meanwhile, whisk together the vinegar, oregano and remaining 2 tbsp. EVOO. Season with salt and pepper.
Season the steak with salt and pepper and broil, turning once, for about 8 minutes for medium-rare. While the steak is broiling, toast the rolls on a baking sheet on the bottom rack for 3 minutes.
Let the steak rest for 5 minutes (if you can spare the extra time), then thinly slice. Toss with the onion and peppers, then the dressing. Serve the pepper steak in the rolls.
