Shape beef into 8 patties, about 4 inches in diameter and 1/4 inch thick. Combine cheese, parsley, bacon, garlic and salt in small bowl and toss to blend. Mound cheese mixture separated evenly on each of 4 patties and top with remaining 4 patties, pinch sides to close.
Heat bacon grease in skillet over medium-high heat until hot. Quickly toss peppers in to brown slightly, remove and set to the side. In same skillet, add burgers and cook for 4-5 minutes on each side.
Remove from heat and top with peppers and a sprinkling of blue cheese. I have served these burgers topped with caramelized onions and it is divine!