Allow the steak to come to room temperature (approx. 20 mins) and pat dry.
Cut 1 head of garlic in half without removing the skins.
Preheat oven to 750°F and then preheat a large skillet until it reaches 400°F.
Remove skillet and add olive oil. Once the oil flows like water ( meaning it has pre-heated well), place the two halves of the head of garlic (cut side down) into the oil.
Top the steak with salt to taste and place into the pan. Then put back into the oven. The skins of the garlic will burn, but will also protect the cloves themselves.
After approximately 3 minutes, flip the steak and place back into oven. After 3 more minutes, remove skillet from oven.
Quickly, remove garlic as well as steak from skillet.
Wrap the steak in aluminum foil and allow to rest for 5-10 minutes.
While the steak is resting, remove all of the cooked garlic from the roasted halves. In a small bowl, use a fork to mash garlic, and mix with the mayonnaise.
Assembling the sandwich can vary from person to person, but we like to slice the focaccia open faced and begin topping. Place a nice helping of the tomato spread on one half, and garlic aioli on the other.
Slice steak and lay on the sandwich as well as a bed of fresh arugula. Stack and enjoy!