Prepare the Herb Sauce: Combine parsley, ½ cup olive oil, red onion, vinegar, garlic, 1 teaspoon salt, and red pepper flakes in a bowl. Stir well and set aside.
Cook the Potatoes: Toss potato wedges with 1 tablespoon olive oil, ¼ teaspoon salt, and ¼ teaspoon pepper in a microwave-safe bowl. Cover and microwave, stirring occasionally, for 5 to 7 minutes until they start to soften. Drain well.
Sear the Steaks: Heat 1 tablespoon olive oil in a 12-inch nonstick skillet over medium-high heat until shimmering. Pat steaks dry with paper towels and season with remaining ½ teaspoon salt and ¼ teaspoon pepper. Place steaks in the skillet and sear without moving for 3 to 5 minutes until browned. Flip, reduce heat to medium, and cook for 5 to 7 minutes until the internal temperature reaches 120–125°F for medium-rare. Transfer to a cutting board, tent with foil, and let rest.
Finish the Potatoes: In the same skillet, add the remaining 2 tablespoons olive oil over medium heat until shimmering. Add potatoes and cook, stirring occasionally, until browned and crisp, about 10 minutes.
Serve: Slice steaks ¼ inch thick and serve alongside crispy potatoes, passing the herb sauce at the table.