London Broil And Portobello Sandwich Recipe

• 1 1/2 lb London broil
• 1/2 c. extra virgin olive oil plus more for brushing steak Salt to taste Freshly-grnd black pepper to taste
• 1/4 c. balsamic vinegar
• 4 x portobello mushroom caps cut in slices
• 1 x Vidalia onion cut in rings
• 1/2 c. mayonnaise
• 1 Tbsp. grated horseradish (or possibly grainy mustard)
• 1/2 c. minced fresh parsley
• 1/2 x lemon juiced
• 4 piece ciabatta bread split horizontally
• 1/4 lb Fontina sliced
• 1/3 c. coarsely-minced arugula leaves - (packed)

Directions