Preheat grill to 350° to 400° (medium-high) heat. Gently combine ground chuck, 1/4 cup Worcestershire sauce, and 1/4 tsp. pepper in a large bowl. Using your hands, gently shape meat into 8 (4-inch) patties (about 3/4 inch thick). Transfer patties to a jelly-roll pan, and drizzle with remaining 1/4 cup Worcestershire sauce. Sprinkle with 1/2 tsp. each salt and pepper. Turn patties over, and sprinkle with remaining salt and pepper.
Grill patties, covered with grill lid, 6 to 8 minutes on each side. Transfer burgers to a platter, and cover loosely with aluminum foil. Let stand 5 minutes.
Meanwhile, grill buns 1 to 2 minutes or until grill marks appear. Serve burgers on buns with tomato slices, Green Tomato Mayonnaise, and baby spinach.