Slice the baguette horizontally and toss with olive oil and kosher salt. Place on a cookie sheet and toast until crostini is golden brown and moist in the middle. Remove from oven and let cool. Grill or oven broil your flank steak and salt to taste. Cook for 15 minutes on each side or until meat is prepared to your liking.
In a skillet fry your onions with a 1/4-cup of water and a dash or Worcestershire sauce for flavor. Set aside and let cool. Roast the garlic and set-aside. Spread roasted garlic on each crostini and top with arugula, flank steak and caramelized onions. Garnish with fresh diced chives.