Rub both sides of the steak with the garlic, patting the garlic to adhere. Sprinkle with the crushed red pepper and season with salt and pepper. Let stand 30 minutes at room temperature.
Preheat the oven to 400 degrees . On a baking sheet, toss the bread, 2 tbsp. EVOO and the salt. Spread in an even layer; bake until crispy, tossing twice, about 20 minutes; let cool. Using your palms, coarsely crush the croutons.
Scrape the garlic off the steak. In a large cast-iron skillet or grill pan, heat 1 tsp. EVOO over medium-high. Cook the steak to desired doneness, about 4 minutes per side for medium-rare. Let rest 10 minutes.
In a large bowl, toss the chicory, celery, onions and currants with the vinegar, lemon zest and juice. Drizzle with the remaining 5 tbsp. EVOO and toss to coat; season. Divide the salad among plates. Thinly slice the steak and arrange on top. Grate the horseradish over the salads to taste.