Remove the steak from the refrigerator 20 minutes before cooking to bring it to room temperature.
Season both sides of the steak evenly with sea salt and black pepper.
Preheat a grill or cast-iron skillet over medium-high heat and lightly coat with avocado oil.
Grill the steak for 4-5 minutes per side for medium-rare, or until it reaches your desired level of doneness.
Transfer the steak to a cutting board and let it rest for at least 5-10 minutes to lock in the juices.
In a small bowl, whisk together the extra virgin olive oil, balsamic vinegar, Dijon mustard, and dried oregano to create the vinaigrette.
In a large salad bowl, combine the mixed greens, halved cherry tomatoes, sliced cucumber, and thinly sliced red onion.
Slice the rested steak against the grain into thin strips.
Arrange the steak strips over the salad and drizzle the balsamic vinaigrette over the top just before serving.