Heat the olive oil in a skillet over medium heat. Add the chopped onion and cook until translucent, about 3-4 minutes.

Add the minced garlic and cook for an additional minute until fragrant.

Add the ground beef to the skillet, breaking it apart with a spatula. Season with salt and pepper. Cook until browned and fully cooked, about 6-8 minutes. Drain any excess fat and set aside.

Butter one side of each slice of bread. On the unbuttered side of two slices, place a slice of cheddar cheese, followed by a generous portion of the cooked ground beef, and then another slice of cheddar cheese. Top with the remaining slices of bread, buttered side facing out.

Heat a skillet over medium heat. Carefully place the assembled sandwiches in the skillet. Cook for about 3-4 minutes on each side, or until the bread is golden brown and the cheese is melted. Press down gently with a spatula to ensure even grilling.

Remove the sandwiches from the skillet and let them cool for a minute before slicing in half. Serve warm and enjoy!