2. Using your hands, lightly shape the ground sirloin into four 1/2-inch thick patties. (Try to leave some air in the burger and avoid packing them too densely.) Season with salt and pepper.
3. Lightly drizzle the red pepper quarters with olive oil.
4. Cook the burgers on both sides over the hot grill for about 5 to 6 minutes per side for medium burgers. At the same time grill the peppers for 2 to 3 minutes on each side.
5. Lightly toast the buns on the grill.
6. Serve the burgers on toasted buns with grilled red peppers, slices of sweet white onion and crumbled blue cheese.