01 - In a skillet set over medium heat, cook the ground beef with onion powder until meat is fully browned, breaking it apart as it cooks. Drain off any excess fat. Stir in ketchup and mustard, then remove the mixture from the heat.
02 - Spread butter on one side of each slice of bread. Place two slices, buttered side down, onto a work surface. Layer with a slice of cheese, an even portion of the seasoned ground beef, pickle slices, and a second slice of cheese. Top each with a remaining bread slice, buttered side facing out.
03 - Preheat skillet over medium heat. Place sandwiches in the skillet and cook for 3 to 4 minutes per side, pressing gently, until the bread is crisp and golden and the cheese is melted.
04 - Remove sandwiches from the skillet, slice in half, and serve immediately while hot.