Blue Cheese Stuffed Burger with Red Onion and Spinach

In a large bowl combine beef, Worcestershire sauce, and pepper. On waxed paper shape beef mixture into eight thin 4-inch-diameter patties. Place 1 tablespoon of the blue cheese into the centers of four of the patties. Top with the remaining four patties; pinch edges to seal.

Brush onion slices with olive oil; sprinkle with salt.

Place burgers and onion slices on the rack of an uncovered grill directly over medium-high heat. Grill 5 minutes per side or until done (160°F to 165°F). Brush cut sides of buns with olive oil. Grill, cut side down, the last minute of grilling.

Serve burgers on buns with grilled onion slices, spinach, and remaining cheese.