¼ cup mayonnaise
2 tablespoons lemon juice
2 tablespoons extra-virgin olive oil
1 teaspoon Dijon mustard
1 teaspoon anchovy paste
1 small clove garlic, grated
½ teaspoon ground pepper, divided
2 tablespoons grated Parmesan cheese
1 pound flank or sirloin steak (about 1 1/4 inches thick), trimmed
¼ teaspoon salt plus a pinch, divided
1 large tomato, chopped
½ cup thinly sliced red onion
1 large head romaine lettuce, cut lengthwise into quarters
Lemon wedges for serving
Preheat grill to medium.
Whisk mayonnaise, lemon juice, oil, mustard, anchovy paste, garlic and 1/4 teaspoon pepper in a small bowl. Stir in Parmesan. Set aside.
Sprinkle both sides of steak with 1/4 teaspoon salt and the remaining 1/4 teaspoon pepper.
Oil the grill rack. Grill the steak, flipping once, until an instant-read thermometer inserted in the thickest part registers 125°F for medium-rare, about 10 minutes. Transfer to a clean cutting board and let rest for 5 minutes. Slice the steak against the grain.
Meanwhile, toss tomato, onion and the remaining pinch of salt in a medium bowl. Arrange romaine on a platter and top with the tomato mixture and the steak. Drizzle with the reserved dressing and serve with lemon wedges, if desired.