Clean the grill grates. You can oil the grates lightly to prevent sticking, but there's enough fat in Wagyu that it's not usually necessary.
In a charcoal grill, create a two-zone fire by placing charcoal on one side while leaving the other empty so you can move the hamburgers to the cooler side if they cook too quickly.
Preheat a gas grill on medium-high until it reaches 375-400°F (190-205℃). If using charcoal, make sure the coals are evenly lit and glowing before adding the patties.
Gently but thoroughly mix the ground beef, salt, pepper, and the optional Worcestershire sauce, minced garlic and onions, and burger seasoning in a large bowl. Avoid overmixing.
Divide the hamburger into 4-6 equal parts, then form the patties. Use your thumb to make a slight depression in the middle of each patty to prevent them from puffing up on the grill. Chill them in the fridge for around 30 minutes to firm up the fat before placing them on the grill.
Place the patties on the hot side of the grill and grill them for 3-4 minutes, undisturbed. Gently flip them, and cook for another 3-4 minutes, or until the internal temperature reads your preferred doneness.
If the burger is cooking too fast, move the patties to the cooler side, away from direct heat. Grilling Wagyu burgers can cause flare-ups thanks to their high fat content. You can also lower the heat at this stage so they cook evenly.
Cooking time varies depending on the thickness of the patties and the desired doneness. The FDA recommendation for ground beef food safety is an internal temperature of 160°F (70°C).