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 square patties. Place on a baking sheet lined with parchment paper and freeze for 30 minutes.
Heat a large griddle or cast iron skillet over medium-high heat. Once hot, place the frozen meat patties on the pan. You might have to cook them in batches. 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 pan and place a slice of cheese on top of each patty and allow to melt.
Toast the buns and place the remaining cheese slices on top of the bottom buns. To assemble the burgers, place a burger patty on top, lettuce, tomato, onion, and pickles. Spread the top buns with mayo and ketchup and place on top of the burgers. Serve immediately.