Season the steak. Pat the steak dry.
Rub with olive oil, salt, pepper, and oregano. Let it sit at room temperature for 20–30 minutes while you prep the salad.
Make the dressing. In a jar, combine olive oil, lemon zest and juice, red wine vinegar, garlic, Dijon, oregano, honey, salt, and pepper. Shake until emulsified.
Taste and adjust salt or lemon as needed.
Prep the vegetables. Chop romaine and arugula. Slice cucumber, tomatoes, red onion, and bell pepper. Halve the olives.
Cut or crumble the feta. Slice the avocado right before serving.
Cook the steak. Heat a cast-iron skillet or grill over high heat until very hot. Cook flank steak 4–5 minutes per side for medium-rare (skirt steak usually needs 3–4 minutes per side). Aim for 130–135°F internal temperature for medium-rare.
Rest and slice. Transfer steak to a board and rest 8–10 minutes.
Slice thinly against the grain so it stays tender.
Assemble the base. In a large bowl, toss romaine and arugula with half the dressing. Spread onto a platter.
Add the toppings. Scatter cucumber, tomatoes, onion, bell pepper, and olives over the greens. Tuck in avocado and feta.
Sprinkle dill and parsley.
Finish with steak and dressing. Arrange sliced steak on top. Drizzle with remaining dressing. Add a pinch of salt and a few grinds of pepper to finish.
Serve. Bring to the table right away so the steak is still warm and the greens stay crisp.