Season the chuck steak on both sides with half of the sea salt and black pepper.
Preheat a grill or cast-iron skillet over medium-high heat and lightly coat with a small amount of oil.
Grill the steak for 4-5 minutes per side until it reaches your desired level of doneness.
Remove the steak from the heat and let it rest for 5 minutes before slicing it into thin strips.
In a large bowl, combine the baby spinach, chickpeas, diced cucumber, halved cherry tomatoes, and minced red onion.
In a small jar or bowl, whisk together the olive oil, lemon juice, dried oregano, and the remaining salt and pepper.
Toss the salad with the dressing, top with the sliced steak and crumbled feta cheese, and serve immediately.