In a large bowl, combine the ground sirloin, salt, pepper, garlic and onion powder until evenly combined. Divide the mixture into 4 equal parts and then shape each into thin patties. Place on a baking sheet lined with parchment paper and freeze for 30 minutes.
Heat an indoor grill pan or outdoor grill over high heat. Once hot, place the frozen meat patties on the grill. Press down with a spatula and cook for about 4 minutes on the first side. Flip over and cook for another 2 to 3 minutes on the second side. Turn off the grill and place a slice of cheese on top of each patty.
In a small bowl, combine the ketchup and relish. Set aside.
Toast the buns and spread each half with mayo.
To assemble the burgers, place a few pickle slices on each bottom half of the buns. Top layer lettuce, tomatoes, onions and a burger patty. Spread some of the ketchup mixture on the top bun and place on top. Serve immediately.