In a large mixing bowl, beat the softened cream cheese until smooth and free of lumps.
Incorporate the sour cream and mayonnaise into the cream cheese, mixing until a uniform consistency is achieved.
Fold in the garlic powder, onion powder, black pepper, and three-quarters of the crumbled bacon.
Transfer the base mixture into a shallow serving dish and smooth the surface with an offset spatula.
Refrigerate the mixture for a minimum of 60 minutes to allow the base to set and flavors to meld.
Just prior to service, distribute the shredded iceberg lettuce in an even layer over the cream base.
Top the lettuce layer with the diced tomatoes, the remaining crumbled bacon, and sliced green onions.
Serve immediately with toasted baguette slices or sturdy crackers.