01 -
Preheat an outdoor grill to medium-high heat.
02 -
In a medium bowl, whisk together Dijon mustard, garlic, Italian seasoning, salt, pepper, and red wine vinegar. Slowly stream in olive oil while whisking to emulsify.
03 -
Add the steak to the marinade, toss to coat thoroughly, and let marinate at room temperature for 15 minutes.
04 -
Lightly oil grill grates. Remove steak from marinade and pat dry. Grill for 4 minutes per side, or until internal temperature reaches 135°F for medium-rare.
05 -
Transfer steak to a cutting board and let rest for 5 minutes. Slice thinly across the grain.
06 -
Divide chopped lettuce and halved cherry tomatoes among serving plates. Drizzle with any juices from the cutting board, top with sliced steak, and finish with a dollop of tzatziki sauce.