Season the steak with olive oil, salt, pepper, garlic powder, and smoked paprika, then let it rest at room temperature while preparing the salad ingredients for even cooking.
Combine romaine, spinach, tomatoes, cucumber, onion, corn, and feta cheese in a large bowl, keeping the avocado separate until serving for the freshest texture.
Whisk together olive oil, balsamic vinegar, Dijon mustard, honey, garlic, salt, and pepper until smooth and fully combined to create the homemade dressing.
Cook the steak in a hot skillet or grill pan for 4–5 minutes per side until browned outside and juicy inside, adjusting slightly for your preferred doneness.
Rest the steak for 10 minutes before slicing thinly against the grain to keep the meat tender and flavorful.
Assemble the salad with sliced steak and avocado on top, then drizzle with dressing right before serving for the best texture and freshness.