In a small saucepan over medium heat, melt the butter. Once melted, add the minced garlic and sauté until fragrant, about 1-2 minutes. Remove from heat and let cool slightly.
In a large mixing bowl, combine the lean ground beef, onion powder, freshly ground pepper, salt, soy sauce, and the cooled garlic butter mixture. Using your hands, gently mix until just combined, being careful not to overwork the meat.
Divide the mixture into equal portions and shape them into patties. Aim for about 6 ounces each, making a slight indentation in the center of each patty to ensure even cooking.
Preheat your grill to medium-high heat. This ensures a nice sear on the outside of the burgers while keeping the inside juicy.
Place the patties on the grill and cook for about 4-5 minutes on one side. Flip them and continue cooking for another 4-5 minutes, or until they reach your desired level of doneness. If you prefer cheese on your burgers, add a slice during the last minute of cooking to melt.
While the burgers are finishing, lightly toast the hamburger buns on the grill for about 1-2 minutes until golden and crisp.
Start with the bottom bun, add the grilled patty, then layer on your sliced tomatoes, lettuce, avocado, and onions. Top it off with a dollop of mayonnaise, ketchup, and mustard before placing the top bun on.
