Preheat oven to 425℉.

Heat a cast iron frying pan over med/high heat for about 2-3 mins. While pan is heating salt & pepper steak. Add butter to pan and once melted carefully place steak in pan and do not move for 4-5 mins. Flip steak and continue cooking for another 4-5 mins (for med rare). Once done place on cutting board to rest for 5 mins before cutting.

Meanwhile peel & cut onions into strips. Place a separate large frying pan over med/high heat for about 1-2 mins. Add oil and onion strips. Stir gently so that slices are covered in oil. Continue stirring gently every few mins until caramelized, about 10-12 mins for a lighter caramelization. Turn off heat & set aside.

Place 1-3 tbsp (depending on taste preferences) on each of the naan. Divide caramelized onions among the 4 breads. Cut steak into cubes & place desired amount on each bread. Top with slices of cheese. Place on cookie sheet and bake in a 425℉ oven for 10 mins.