Trim excess fat from the steak and pat dry with paper towels. Slice the bell peppers into 1/2-inch strips and thinly slice the onion. Halve the cherry tomatoes and slice the cucumber. Place the mixed greens in a large bowl and refrigerate until ready to assemble.

Marinate steak

Combine the steak marinade ingredients (3 tbsp olive oil, 2 tbsp balsamic vinegar, 1 tbsp soy sauce, 1 tsp Worcestershire, minced garlic, oregano, red pepper flakes) in a shallow dish or resealable bag. Add the steak and turn to coat. Marinate at room temperature for 20 minutes or in the refrigerator for up to 2 hours. Remove steak from the refrigerator 20 minutes before cooking to come closer to room temperature if chilled.

Cook peppers and onions

Heat 1 tbsp olive oil in a large skillet or cast-iron pan over medium-high heat. Add the bell peppers and onions, season with 1/2 tsp salt and 1/4 tsp black pepper, and sauté until softened and slightly charred, about 6–8 minutes, stirring occasionally. Remove from the pan and keep warm.

Grill or sear steak

Heat a grill or heavy skillet to high. Brush the steak lightly with 1 tbsp olive oil and season both sides with 1/2 tsp salt and a pinch of black pepper. Grill or sear the steak until desired doneness: about 3–4 minutes per side for medium-rare on a 1/2-inch to 3/4-inch steak, longer for thicker cuts. Use an instant-read thermometer for accuracy (125–130°F for medium-rare, 135°F medium). Let the steak rest on a cutting board for 5–10 minutes to retain juices.

Slice steak and assemble salad

Slice the rested steak thinly across the grain. In a large bowl, combine the chilled mixed greens, sautéed peppers and onions, cherry tomatoes, cucumber slices, and chopped parsley. Arrange the salad on plates or a platter and top with sliced steak.

Balsamic dressing (side)

In a small jar or bowl, combine 4 tbsp extra-virgin olive oil, 2 tbsp balsamic vinegar, 1 tsp Dijon mustard, 1 tsp honey, 1/2 tsp minced garlic, 1/2 tsp salt and 1/4 tsp black pepper. Whisk or shake vigorously until emulsified. Taste and adjust seasoning. Serve the dressing on the side or drizzle lightly over the assembled salad just before serving.