Cook the steak to your preference, then set aside to rest. For a 2" steak, that takes a mere 3–4 minutes per side in a ripping hot cast iron pan with a little oil, or same timing on a hot grill. I shoot for 125° F internal temperature, then allow to rest off heat.
Mix the dressing in your salad serving bowl. Start with a dab of Dijon mustard (1/2 teaspoon or so), salt, and wine vinegar. While whisking, drizzle in the olive oil. Taste with a leaf of spinach and adjust to your preference with more vinegar or oil. Add a few grinds of fresh black pepper.
Put the spinach in the salad bowl with the dressing, add the avocado, golden raisins and toss to combine. Plate and top with parmesan and steak slices.