Whisk 3 tbsp olive oil, balsamic, Dijon, honey, garlic, lemon juice, paprika, salt, and pepper until glossy.
Coat the steak with 2 tbsp of the vinaigrette. Let it stand 10 minutes; reserve the rest for dressing.
Heat a large skillet over medium-high. Add 1 tbsp olive oil and swirl to coat.
Sear steak 3–4 minutes per side for medium-rare. Transfer to a board and rest 5 minutes.
Slice steak thinly against the grain.
Combine greens, tomatoes, cucumber, red onion, avocado, and parsley in a large bowl.
Drizzle with remaining vinaigrette and toss gently to coat. Adjust salt and pepper if needed.
Top with sliced steak, then scatter blue cheese and croutons. Serve right away.