Preheat the oven to 400 degrees F. Line a baking sheet with a piece of parchment or foil. Place the bacon side-by-side and transfer to the oven to cook for 15 to 20 minutes, until golden brown. Carefully remove the bacon from the baking sheet and transfer to a bed of paper towels to drain. In a small bowl, mix together the sour cream, blue cheese, dried mustard, garlic powder and a few pinches of salt.
Place the slices of toast in the toaster and toast until lightly golden brown. To assemble the sandwich, liberally add the blue cheese dressing to both sides of bread. Stack the lettuce, tomato slices and bacon on top of one another. Place the second half of bread on top and slice the sandwich in half.