Heat a grill pan or grill to medium-high heat. Lightly oil the grill grates.
Set 2 scallions aside. Drizzle the remaining scallions on a plate with the olive oil and sprinkle with salt and pepper. Add the oiled scallions to the grill pan and cook until slightly charred, 2 to 3 minutes per side. Set aside to cool completely, then finely chop. Thinly slice the whites and light greens of the remaining 2 scallions and set aside for garnish.
Combine the cream cheese, mayonnaise, sour cream, Worcestershire, garlic salt, onion powder and 1/4 teaspoon ground pepper in a medium bowl. Beat with an electric mixer until smooth. Stir in the grilled scallions. Transfer to a serving bowl and garnish with the fresh sliced scallions. Serve right away or chill.