Prepare the Patties: In a large bowl, mix the ground beef with salt and black pepper. Divide the mixture into 4 equal parts and shape into patties.
Cook the Patties: Preheat a grill or skillet over medium-high heat. Cook the patties for 4-5 minutes on each side, or until they reach your desired doneness. In the last minute of cooking, place a slice of cheese on each patty to melt.
Grill the Onions: While the patties are cooking, brush the onion rings with olive oil and grill for 2-3 minutes on each side until they are tender and have grill marks.
Assemble the Platter: Arrange the cooked patties, buns, grilled onions, lettuce, tomato slices, pickles, avocado, and condiments on a large serving tray.
Serve: Let everyone build their own burger with their favorite toppings and condiments.