Begin by preparing the steak. Season your sirloin with salt and pepper to taste.
Heat the olive oil in a skillet over medium heat. Once heated, add the steak and sear on each side for 4-5 minutes or until your preferred level of doneness is achieved.
After cooking, allow the steak to rest for 5 minutes before thinly slicing.
While the steak is resting, let’s get the grilled cheese going. Butter one side of each slice of bread.
Place two slices of bread, buttered side down, in a clean skillet over medium heat.
Layer a slice of cheddar and a slice of mozzarella on each piece of bread. Then, distribute the sliced steak evenly between the two sandwiches.
Top each sandwich with the remaining cheese slices and the remaining bread, buttered side up.
Cook until the bread is golden and the cheese is melting, flipping halfway.