How to Make It
Preheat oven to 400°F. Toss together bread and 3 tablespoons of the oil on a rimmed baking sheet. Bake until toasted, 10 to 12 minutes.
Meanwhile, heat a grill pan coated with cooking spray over medium-high. Stir together black pepper, paprika, garlic powder, and 1 teaspoon of the salt in a small bowl; sprinkle evenly over steak. Coat bell peppers with cooking spray. Add steak, bell peppers, and shallots to pan. Cook steak to desired degree of doneness, about 7 minutes per side for medium. Cook bell peppers, turning occasionally, until char marks appear, 10 to 15 minutes. Cook shallots until tender, 4 to 5 minutes per side. Remove steak, bell peppers, and shallots from pan as they finish cooking. Let stand 5 minutes. Cut steak thinly across the grain. Cut bell peppers into strips, discarding stems and seeds. Cut shallots vertically into slices.
Whisk together vinegar, remaining 6 tablespoons oil, and remaining 1/2 teaspoon salt in a large bowl. Add toasted bread; toss to coat. Add steak, bell peppers, shallots, and arugula; toss gently to coat. Divide salad evenly among 4 plates. Sprinkle with cheese, if desired.