Add the vinegar, chopped red onion, mustard, honey, garlic, salt and pepper to a food processor or blender and blend until thoroughly combined. With the motor running, drizzle in the oil--slowly at first, then in a thin, steady stream--until all of the oil is incorporated and the mixture is smooth. Set the vinaigrette aside until ready to use.
Heat a skillet over medium heat and cook the bacon until crisp. Drain the bacon on paper towels and, when cool, crumble and set aside.
Remove the root end from the lettuce and cut the head into 4 wedges. Divide the wedges among 4 plates. In a saucepan, heat the vinaigrette over medium heat for 2 minutes. Dress each wedge with 2 tablespoons of the dressing. Top with the bacon, sliced red onion and scallions.
Poach the eggs: Line a plate with paper towels. Fill a medium saucepan with water and bring to a simmer, then add 2 teaspoons of vinegar. Crack an egg into a small cup and gently slide it into the water. Using a slotted spoon, nudge the egg white closer to the yolk. When the white is cooked, carefully remove the egg from the water. Drain on the paper towels. Repeat with the remaining eggs. Top each salad with a poached egg and serve.