Heat a dry large skillet, (cast iron is best) over medium-high. Using a sharp knife, lightly score the steak on both sides in a crosshatch pattern. Season generously with salt and pepper, then rub all over with vegetable oil.
Cook steak, turning once or twice to brown evenly, until medium-rare and lightly charred, 8−10 minutes. Transfer steak to a cutting board and let rest at least 15 minutes; reserve skillet
While cooking the steak, place onion in a small bowl. cover with cold water and set aside.
In a blender, combine mustard and lemon juice. With motor running, stream in ½ cup olive oil, then gradually add Parmesan. Stream in 1 tbsp. cold water and blend until dressing is smooth and thick. Season with salt and pepper.
Heat reserved skillet over medium heat. Slice Country Harvest™ Everything Bagels in half and drizzle cut halves with olive oil. Working with 1 bagel at a time, cook, cut side down, until golden brown and crisp, about 5 minutes each.
Place bread, cut side up, on a plate and drizzle with one-third of dressing. Top with arugula; drain reserved onion and scatter over arugula. Season with salt and pepper and drizzle with half of the remaining dressing. Thinly slice steak and arrange over dressed arugula. Drizzle with remaining dressing, season with more salt and enjoy!