Heat 1 tablespoon olive oil in a large skillet over high heat.
Add the onion and bacon and cook until the bacon is crispy.
Remove the onion and bacon from the pan.
Add the balsamic vinegar and 1 tablespoon olive oil to the skillet and reduce for 2 to 3 minutes.
Remove from the heat and set aside.
Brush the romaine with the remaining 2 tablespoons olive oil.
Place on the grill cut-side down and quickly sear until grill marks are visible. Set aside. For each serving, place a half head of romaine cut-side up on a plate and drizzle the balsamic dressing on top.
Sprinkle with blue cheese and the bacon and onion, and garnish with cracked black pepper. Photograph by Yunhee Kim