Prepare a charcoal or gas grill for direct grilling over medium-high heat. In a large bowl, mix together the beef, yellow onion, garlic, salt, pepper and Worcestershire sauce. Form the mixture into 4 patties, each about ¾-inch thick with an indentation in the center.
Grill the hamburgers directly over medium-high heat, turning once, 3 to 5 minutes per side. Check for doneness by cutting into a hamburger near the center or testing with an instant-read thermometer. For a well done burger, no pink should show on the inside, and the internal temperature should register at least 160°F on an instant-read thermometer. If making cheeseburgers, place a slice of cheese on top of each hamburger during the last 3 minutes of cooking.
During the last 2 to 3 minutes of cooking, toast the hamburger buns, cut side down, on the grill. Serve the hamburgers on burger buns with toppings and condiments as desired.