- 5 tablespoons extra-virgin olive oil, divided
- 3 cups presliced fresh bell pepper-and-onion mix (10 ounces)
- 2 teaspoons white-wine vinegar plus 2 tablespoons, divided
- 1 pound shaved sandwich steak
- ¾ teaspoon ground pepper, divided, plus more to taste
- ¼ teaspoon salt, divided
- ½ cup shredded Gruyère or provolone cheese
- 8 cups baby arugula (5 ounces)
- 4 slices crusty whole-wheat bread ( ½ inch thick), lightly toasted
- 8 teaspoons prepared horseradish aioli or horseradish sauce
- Heat 1 tablespoon oil in a large skillet over medium-high heat. Add peppers and onions and cook, stirring often, until softened and starting to brown in spots, 5 to 7 minutes. Stir in 2 teaspoons vinegar. Transfer the vegetables to a bowl.
- Add 1 tablespoon oil to the pan. Add steak, season with ½ teaspoon pepper and ⅛ teaspoon salt and cook, stirring and pulling apart with tongs or a fork, until no longer pink, 3 to 4 minutes. Return the vegetables to the pan, stir to combine. Sprinkle with cheese. Cover and remove from heat.
- Toss arugula in a large bowl with the remaining 3 tablespoons oil, 2 tablespoons vinegar, ¼ teaspoon pepper and ⅛ teaspoon salt.
- Spread each piece of bread with 2 teaspoons aioli (or sauce) and top with one-fourth (about 1 cup) of the steak mixture. Serve the tartines with the arugula salad. Sprinkle with more pepper, if desired.