To make the dressing, in a medium bowl, combine the balsamic vinegar, olive oil, lemon juice, and Italian seasoning. Season with salt and black pepper, to taste, and whisk to combine. Set aside.

Place the steak into a large, sealable freezer bag. Pour half of the balsamic dressing on top and seal tightly. Gently turn the bag to make sure the steak is thoroughly coated in the marinade. Marinate the steak for at least 30 minutes at room temperature (but not more than 2 hours) or place in the refrigerator overnight. Transfer the remaining half of the dressing to an airtight container and set aside until ready to use.

When ready to prepare the salad, preheat oven to 200C/400F/Gas 6.

Heat 1 tablespoon of olive oil in a large oven-safe skillet over high heat. Use tongs to remove the steak from the marinade and discard the bag and any marinade inside. Add the steak to the hot skillet and sear on all sides, approximately 2 minutes per side.

Place the skillet into the pre-heated oven and roast to the desired level of doneness. Approximately 8 minutes for medium-rare. Use an instant-read thermometer to check for doneness. The steak should be a few degrees below the desired temp (e.g., 60C/135F for medium-rare) when removed from the oven. The internal temp will continue to rise while resting.

Remove steak from oven and transfer to plate. Cover loosely and set aside to rest for 5-10 minutes.

Meanwhile, toss the freshly chopped avocado with the lemon juice to prevent browning. Set aside.

Layer the mixed salad greens, cucumber, tomatoes, red onion, olives, and avocado on a large serving platter and season with salt and black pepper, to taste.

Once the steak is rested, slice into thin strips and place on top of the salad. Top with crumbled Feta cheese and serve immediately with the remaining balsamic dressing on the side. Enjoy!