Preheat your skillet or griddle over medium-high heat for about 5 minutes.
While the skillet is heating, take the ground beef and divide it into 4 equal portions (about 4 ounces each) without forming a patty shape; just loosely form them into balls.
Once the skillet is hot, add the vegetable oil and let it heat for a minute.
Place the beef balls onto the skillet. Using a spatula, smash each ball down into a patty shape, pressing down firmly to create a thin layer.
Season each patty with salt and black pepper.
Cook the patties for about 2-3 minutes, or until the bottom is browned and crispy. Flip the patties and add a slice of cheese on top if desired.
Cook for another 1-2 minutes until the cheese is melted and the internal temperature reaches 160°F (71°C).
While the patties are cooking, toast the burger buns on a separate skillet or directly in the oven until golden brown.
Remove the patties and buns from heat. Assemble each burger by placing the lettuce, tomato, and pickles on the bottom half of the bun, followed by the patty.
Add ketchup and mustard to taste. Top with the other half of the bun.
Serve immediately while still hot.