Heat oven to 400° F. On a rimmed baking sheet, toss the bread with 1½ tablespoons oil. Bake in an even layer until golden and crisp, 5 to 6 minutes.
Transfer the bread to a bowl and toss with the parsley and capers; set aside.
Meanwhile, heat the remaining 1½ tablespoons of oil and the garlic in a large skillet (preferably cast iron) over medium-high heat.
Season the steak with salt and pepper and add to the skillet, cooking until browned, 2 to 3 minutes per side. Transfer the steak and garlic to the baking sheet.
Place the sheet in oven and roast that steak to desired doneness, 6 to 8 minutes for medium-rare. Let rest at least 5 minutes before slicing.
Meanwhile, add the cauliflower and ½ cup water to the skillet and cook, covered, until it’s tender and the water has evaporated, 6 to 7 minutes. Sprinkle with the reserved crumbs and serve with the steak and garlic.