For the steak: Let the steak rest at room temperature for 20 minutes. Preheat a grill pan or outdoor grill to high.
Rub both sides of the steak with oil and sprinkle liberally with salt and pepper. Grill the steak until lightly charred, 3 to 4 minutes per side for medium-rare (cook longer for medium or well-done steak). Transfer to a cutting board and let rest 10 minutes.
For the yellow pepper chimichurri: Combine the bell pepper, parsley, oregano, garlic, oil, vinegar, salt and black pepper in a food processor. Process until well mixed but still a little chunky. Transfer to a small bowl.
Cut the steak into thin slices across the grain. Serve with the chimichurri.