01 - In a mixing bowl, combine the ground beef, basil pesto, minced garlic, salt, and black pepper. Gently fold the mixture until just incorporated, being careful not to overwork the meat. Divide into 4 equal portions and shape each into a patty about 3/4 inch thick, pressing a slight indentation in the center to prevent puffing during cooking.
02 - In a small bowl, whisk together the mayonnaise, finely minced garlic, lemon juice, and chopped parsley. Season with salt and pepper to taste. Cover and refrigerate to allow the flavors to meld while you cook the burgers.
03 - Preheat a grill or cast-iron skillet over medium-high heat. Place the burger buns cut-side down on the cooking surface and toast for 1 to 2 minutes until golden brown and lightly crisp. Remove and set aside.
04 - Place the patties on the preheated grill or skillet and cook for 4 to 5 minutes per side, or until they reach your desired level of doneness. During the last minute of cooking, lay a slice of provolone or mozzarella cheese on each patty and cover with a lid or foil to allow the cheese to melt evenly.
05 - Spread a generous layer of creamy garlic mayo on the bottom half of each toasted bun. Layer on a lettuce leaf, followed by the cheesy patty, a tomato slice, and a few red onion rings. Add an extra spread of mayo on the top bun if desired, then close the burger.
06 - Serve the burgers immediately while hot and juicy, alongside your favorite sides such as fries, a green salad, or coleslaw.