Ingredients

  • 1 1/2 pound London broil
  • 1/2 cup olive oil, plus more for brushing steak
  • Salt and pepper
  • 1/4 cup balsamic vinegar
  • 4 portobello mushroom caps, cut in slices
  • 1 Vidalia onion, cut in rings
  • 1/2 cup mayonnaise
  • 1 tablespoon grated horseradish or grainy mustard
  • 1/2 cup chopped fresh parsley
  • 1/2 lemon, juiced
  • 4 pieces ciabatta bread, split horizontally
  • 1/4 pound Fontina, sliced
  • 1/3 cup (packed) coarsely chopped arugula leaves

Method

  • Preheat oven broiler for 5 minutes.
  • Brush both sides of London broil with olive oil and season with salt and pepper.
  • Place the steak on a broiler pan and broil about 4-inches from the heat source, about 5 minutes per side.
  • Lay the portobellos and onions in a single layer on a sheet pan lined with aluminum foil.
  • Drizzle with oil and vinegar then put in the oven and roast for 10 minutes.
  • Remove the steak to a cutting board.
  • Let rest for 5 minutes then slice the steak thinly against the grain.
  • In a small bowl, combine mayonnaise, horseradish, parsley, and lemon juice.
  • Spread mayonnaise mixture on both sides of the split ciabatta.
  • Lay several slices of steak on the bread and mound with a bit of mushrooms and onions.
  • Cover with a couple of slices of cheese.
  • Garnish with arugula, and serve.