Combine beef, spinach, Worcestershire, salt, and pepper (if the meat starts to warm up while you mix it, put it back in the fridge).
Roll beef into balls and then flatten into a thin patty on top of wax paper, about 1⁄4 inch high and about 5 inches in diame-ter.
Place about 1 oz cheese on top of patties. Put a second patty on top of cheese. Pinch edges together. Re-cover with wax paper and refrigerate for at least 10 minutes. Grill chilled patties.